[InstSimplify] Add more poison folding optimizations

This adds more poison folding optimizations to InstSimplify.

Since all binary operators propagate poison, these are fine.

Also, the precondition of `select cond, undef, x` -> `x` is relaxed to allow the case when `x` is undef.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D104661

llvm/lib/Analysis/InstructionSimplify.cpp

@@ -734,6 +734,11 @@ static Value *SimplifySubInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
   if (Constant *C = foldOrCommuteConstant(Instruction::Sub, Op0, Op1, Q))
     return C;
 
+  // X - poison -> poison
+  // poison - X -> poison
+  if (isa<PoisonValue>(Op0) || isa<PoisonValue>(Op1))
+    return PoisonValue::get(Op0->getType());
+
   // X - undef -> undef
   // undef - X -> undef
   if (Q.isUndefValue(Op0) || Q.isUndefValue(Op1))
@@ -869,6 +874,10 @@ static Value *SimplifyMulInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
   if (Constant *C = foldOrCommuteConstant(Instruction::Mul, Op0, Op1, Q))
     return C;
 
+  // X * poison -> poison
+  if (isa<PoisonValue>(Op1))
+    return Op1;
+
   // X * undef -> 0
   // X * 0 -> 0
   if (Q.isUndefValue(Op1) || match(Op1, m_Zero()))
@@ -955,6 +964,11 @@ static Value *simplifyDivRem(Instruction::BinaryOps Opcode, Value *Op0,
     }
   }
 
+  // poison / X -> poison
+  // poison % X -> poison
+  if (isa<PoisonValue>(Op0))
+    return Op0;
+
   // undef / X -> 0
   // undef % X -> 0
   if (Q.isUndefValue(Op0))
@@ -1241,6 +1255,10 @@ static Value *SimplifyShift(Instruction::BinaryOps Opcode, Value *Op0,
   if (Constant *C = foldOrCommuteConstant(Opcode, Op0, Op1, Q))
     return C;
 
+  // poison shift by X -> poison
+  if (isa<PoisonValue>(Op0))
+    return Op0;
+
   // 0 shift by X -> 0
   if (match(Op0, m_Zero()))
     return Constant::getNullValue(Op0->getType());
@@ -1984,6 +2002,10 @@ static Value *SimplifyAndInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
   if (Constant *C = foldOrCommuteConstant(Instruction::And, Op0, Op1, Q))
     return C;
 
+  // X & poison -> poison
+  if (isa<PoisonValue>(Op1))
+    return Op1;
+
   // X & undef -> 0
   if (Q.isUndefValue(Op1))
     return Constant::getNullValue(Op0->getType());
@@ -2152,6 +2174,10 @@ static Value *SimplifyOrInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
   if (Constant *C = foldOrCommuteConstant(Instruction::Or, Op0, Op1, Q))
     return C;
 
+  // X | poison -> poison
+  if (isa<PoisonValue>(Op1))
+    return Op1;
+
   // X | undef -> -1
   // X | -1 = -1
   // Do not return Op1 because it may contain undef elements if it's a vector.
@@ -3689,6 +3715,11 @@ static Value *SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
   if (match(RHS, m_NaN()))
     return ConstantInt::get(RetTy, CmpInst::isUnordered(Pred));
 
+  // fcmp pred x, poison and  fcmp pred poison, x
+  // fold to poison
+  if (isa<PoisonValue>(LHS) || isa<PoisonValue>(RHS))
+    return PoisonValue::get(RetTy);
+
   // fcmp pred x, undef  and  fcmp pred undef, x
   // fold to true if unordered, false if ordered
   if (Q.isUndefValue(LHS) || Q.isUndefValue(RHS)) {
@@ -4156,6 +4187,10 @@ static Value *SimplifySelectInst(Value *Cond, Value *TrueVal, Value *FalseVal,
       if (auto *FalseC = dyn_cast<Constant>(FalseVal))
         return ConstantFoldSelectInstruction(CondC, TrueC, FalseC);
 
+    // select poison, X, Y -> poison
+    if (isa<PoisonValue>(CondC))
+      return PoisonValue::get(TrueVal->getType());
+
     // select undef, X, Y -> X or Y
     if (Q.isUndefValue(CondC))
       return isa<Constant>(FalseVal) ? FalseVal : TrueVal;
@@ -4183,15 +4218,20 @@ static Value *SimplifySelectInst(Value *Cond, Value *TrueVal, Value *FalseVal,
   if (TrueVal == FalseVal)
     return TrueVal;
 
+  // If the true or false value is poison, we can fold to the other value.
   // If the true or false value is undef, we can fold to the other value as
   // long as the other value isn't poison.
-  // select ?, undef, X -> X
-  if (Q.isUndefValue(TrueVal) &&
-      isGuaranteedNotToBeUndefOrPoison(FalseVal, Q.AC, Q.CxtI, Q.DT))
+  // select ?, poison, X -> X
+  // select ?, undef,  X -> X
+  if (isa<PoisonValue>(TrueVal) ||
+      (Q.isUndefValue(TrueVal) &&
+       isGuaranteedNotToBePoison(FalseVal, Q.AC, Q.CxtI, Q.DT)))
     return FalseVal;
-  // select ?, X, undef -> X
-  if (Q.isUndefValue(FalseVal) &&
-      isGuaranteedNotToBeUndefOrPoison(TrueVal, Q.AC, Q.CxtI, Q.DT))
+  // select ?, X, poison -> X
+  // select ?, X, undef  -> X
+  if (isa<PoisonValue>(FalseVal) ||
+      (Q.isUndefValue(FalseVal) &&
+       isGuaranteedNotToBePoison(TrueVal, Q.AC, Q.CxtI, Q.DT)))
     return TrueVal;
 
   // Deal with partial undef vector constants: select ?, VecC, VecC' --> VecC''
@@ -4213,11 +4253,11 @@ static Value *SimplifySelectInst(Value *Cond, Value *TrueVal, Value *FalseVal,
       // one element is undef, choose the defined element as the safe result.
       if (TEltC == FEltC)
         NewC.push_back(TEltC);
-      else if (Q.isUndefValue(TEltC) &&
-               isGuaranteedNotToBeUndefOrPoison(FEltC))
+      else if (isa<PoisonValue>(TEltC) ||
+               (Q.isUndefValue(TEltC) && isGuaranteedNotToBePoison(FEltC)))
         NewC.push_back(FEltC);
-      else if (Q.isUndefValue(FEltC) &&
-               isGuaranteedNotToBeUndefOrPoison(TEltC))
+      else if (isa<PoisonValue>(FEltC) ||
+               (Q.isUndefValue(FEltC) && isGuaranteedNotToBePoison(TEltC)))
         NewC.push_back(TEltC);
       else
         break;

llvm/test/Transforms/InstCombine/and-narrow.ll

@@ -177,7 +177,7 @@ define <2 x i16> @zext_lshr_vec_overshift(<2 x i8> %x) {
 
 define <2 x i16> @zext_lshr_vec_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @zext_lshr_vec_undef(
-; CHECK-NEXT:    ret <2 x i16> zeroinitializer
+; CHECK-NEXT:    ret <2 x i16> poison
 ;
   %z = zext <2 x i8> %x to <2 x i16>
   %b = lshr <2 x i16> %z, undef
@@ -202,7 +202,7 @@ define <2 x i16> @zext_shl_vec_overshift(<2 x i8> %x) {
 
 define <2 x i16> @zext_shl_vec_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @zext_shl_vec_undef(
-; CHECK-NEXT:    ret <2 x i16> zeroinitializer
+; CHECK-NEXT:    ret <2 x i16> poison
 ;
   %z = zext <2 x i8> %x to <2 x i16>
   %b = shl <2 x i16> %z, undef

llvm/test/Transforms/InstCombine/getelementptr.ll

@@ -496,7 +496,7 @@ define void @test25() {
 ; CHECK-LABEL: @test25(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    store i64 poison, i64* null, align 536870912
-; CHECK-NEXT:    tail call void @foo25(i32 0, i64 0)
+; CHECK-NEXT:    tail call void @foo25(i32 0, i64 poison)
 ; CHECK-NEXT:    unreachable
 ;
 entry:

llvm/test/Transforms/InstCombine/select-binop-cmp.ll

@@ -31,7 +31,7 @@ define i32 @select_xor_icmp2(i32 %x, i32 %y, i32 %z) {
 define i32 @select_xor_icmp_meta(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_xor_icmp_meta(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[Z:%.*]], i32 [[Y:%.*]], !prof !0
+; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[Z:%.*]], i32 [[Y:%.*]], !prof [[PROF0:![0-9]+]]
 ; CHECK-NEXT:    ret i32 [[C]]
 ;
   %A = icmp eq i32 %x, 0
@@ -1267,12 +1267,10 @@ define i32 @select_replace_udiv_speculatable(i32 %x, i32 %y) {
 }
 
 ; We can't replace %x by 0 here, because that would cause UB. However,
-; replacing the udiv result by poisong is fine.
+; replacing the udiv result by poison is fine.
 define i32 @select_replace_udiv_non_speculatable(i32 %x, i32 %y) {
 ; CHECK-LABEL: @select_replace_udiv_non_speculatable(
-; CHECK-NEXT:    [[C:%.*]] = icmp eq i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[S:%.*]] = select i1 [[C]], i32 poison, i32 [[Y:%.*]]
-; CHECK-NEXT:    ret i32 [[S]]
+; CHECK-NEXT:    ret i32 [[Y:%.*]]
 ;
   %c = icmp eq i32 %x, 0
   %div = udiv i32 %y, %x

llvm/test/Transforms/InstSimplify/ConstProp/poison.ll

@@ -115,10 +115,9 @@ define void @other_ops(i8 %x) {
   ret void
 }
 
-; TODO: these must be folded into poison; D92270
 define void @logicalops_i1(i1 %x) {
 ; CHECK-LABEL: @logicalops_i1(
-; CHECK-NEXT:    call void (...) @use(i1 true, i1 false)
+; CHECK-NEXT:    call void (...) @use(i1 poison, i1 poison)
 ; CHECK-NEXT:    ret void
 ;
   %i1 = or i1 %x, poison

llvm/test/Transforms/InstSimplify/and.ll

@@ -1,11 +1,9 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -instsimplify -S | FileCheck %s
 
-; TODO: this should be poison
-
 define i32 @poison(i32 %x) {
 ; CHECK-LABEL: @poison(
-; CHECK-NEXT:    ret i32 0
+; CHECK-NEXT:    ret i32 poison
 ;
   %v = and i32 %x, poison
   ret i32 %v

llvm/test/Transforms/InstSimplify/fcmp.ll

@@ -1,10 +1,9 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -instsimplify -S | FileCheck %s
 
-; TODO: these should be poison
 define i1 @poison(float %x) {
 ; CHECK-LABEL: @poison(
-; CHECK-NEXT:    ret i1 false
+; CHECK-NEXT:    ret i1 poison
 ;
   %v = fcmp oeq float %x, poison
   ret i1 %v
@@ -12,7 +11,7 @@ define i1 @poison(float %x) {
 
 define i1 @poison2(float %x) {
 ; CHECK-LABEL: @poison2(
-; CHECK-NEXT:    ret i1 true
+; CHECK-NEXT:    ret i1 poison
 ;
   %v = fcmp ueq float %x, poison
   ret i1 %v

llvm/test/Transforms/InstSimplify/mul.ll

@@ -42,11 +42,9 @@ define <2 x i8> @mul_by_0_vec_undef_elt(<2 x i8> %a) {
   ret <2 x i8> %b
 }
 
-; TODO: this should be poison
-
 define i32 @poison(i32 %x) {
 ; CHECK-LABEL: @poison(
-; CHECK-NEXT:    ret i32 0
+; CHECK-NEXT:    ret i32 poison
 ;
   %v = mul i32 %x, poison
   ret i32 %v

llvm/test/Transforms/InstSimplify/or.ll

@@ -292,11 +292,9 @@ define <2 x i1> @or_with_not_op_commute4(<2 x i1> %a, <2 x i1> %b) {
   ret <2 x i1> %r
 }
 
-; TODO: this should be poison
-
 define i32 @poison(i32 %x) {
 ; CHECK-LABEL: @poison(
-; CHECK-NEXT:    ret i32 -1
+; CHECK-NEXT:    ret i32 poison
 ;
   %v = or i32 %x, poison
   ret i32 %v

llvm/test/Transforms/InstSimplify/select-inseltpoison.ll

@@ -965,8 +965,6 @@ define <vscale x 2 x i1> @ignore_scalable_undef(<vscale x 2 x i1> %cond) {
   ret <vscale x 2 x i1> %s
 }
 
-; TODO: these can be optimized more
-
 define i32 @poison(i32 %x, i32 %y) {
 ; CHECK-LABEL: @poison(
 ; CHECK-NEXT:    ret i32 [[X:%.*]]
@@ -977,8 +975,7 @@ define i32 @poison(i32 %x, i32 %y) {
 
 define i32 @poison2(i1 %cond, i32 %x) {
 ; CHECK-LABEL: @poison2(
-; CHECK-NEXT:    [[V:%.*]] = select i1 [[COND:%.*]], i32 poison, i32 [[X:%.*]]
-; CHECK-NEXT:    ret i32 [[V]]
+; CHECK-NEXT:    ret i32 [[X:%.*]]
 ;
   %v = select i1 %cond, i32 poison, i32 %x
   ret i32 %v
@@ -986,8 +983,7 @@ define i32 @poison2(i1 %cond, i32 %x) {
 
 define i32 @poison3(i1 %cond, i32 %x) {
 ; CHECK-LABEL: @poison3(
-; CHECK-NEXT:    [[V:%.*]] = select i1 [[COND:%.*]], i32 [[X:%.*]], i32 poison
-; CHECK-NEXT:    ret i32 [[V]]
+; CHECK-NEXT:    ret i32 [[X:%.*]]
 ;
   %v = select i1 %cond, i32 %x, i32 poison
   ret i32 %v
@@ -995,8 +991,7 @@ define i32 @poison3(i1 %cond, i32 %x) {
 
 define <2 x i32> @poison4(<2 x i1> %cond, <2 x i32> %x) {
 ; CHECK-LABEL: @poison4(
-; CHECK-NEXT:    [[V:%.*]] = select <2 x i1> [[COND:%.*]], <2 x i32> [[X:%.*]], <2 x i32> poison
-; CHECK-NEXT:    ret <2 x i32> [[V]]
+; CHECK-NEXT:    ret <2 x i32> [[X:%.*]]
 ;
   %v = select <2 x i1> %cond, <2 x i32> %x, <2 x i32> poison
   ret <2 x i32> %v

llvm/test/Transforms/InstSimplify/select.ll

@@ -957,8 +957,7 @@ declare i32 @llvm.cttz.i32(i32, i1 immarg)
 ; Partial undef scalable vectors should be ignored.
 define <vscale x 2 x i1> @ignore_scalable_undef(<vscale x 2 x i1> %cond) {
 ; CHECK-LABEL: @ignore_scalable_undef(
-; CHECK-NEXT:    [[S:%.*]] = select <vscale x 2 x i1> [[COND:%.*]], <vscale x 2 x i1> undef, <vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0)
-; CHECK-NEXT:    ret <vscale x 2 x i1> [[S]]
+; CHECK-NEXT:    ret <vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0)
 ;
   %vec = insertelement <vscale x 2 x i1> undef, i1 true, i32 0
   %s = select <vscale x 2 x i1> %cond, <vscale x 2 x i1> undef, <vscale x 2 x i1> %vec
@@ -1036,8 +1035,6 @@ define <2 x i32> @vec_select_no_equivalence(<2 x i32> %x, <2 x i32> %y) {
   ret <2 x i32> %s
 }
 
-; TODO: these can be optimized more
-
 define i32 @poison(i32 %x, i32 %y) {
 ; CHECK-LABEL: @poison(
 ; CHECK-NEXT:    ret i32 [[X:%.*]]
@@ -1048,8 +1045,7 @@ define i32 @poison(i32 %x, i32 %y) {
 
 define i32 @poison2(i1 %cond, i32 %x) {
 ; CHECK-LABEL: @poison2(
-; CHECK-NEXT:    [[V:%.*]] = select i1 [[COND:%.*]], i32 poison, i32 [[X:%.*]]
-; CHECK-NEXT:    ret i32 [[V]]
+; CHECK-NEXT:    ret i32 [[X:%.*]]
 ;
   %v = select i1 %cond, i32 poison, i32 %x
   ret i32 %v
@@ -1057,8 +1053,7 @@ define i32 @poison2(i1 %cond, i32 %x) {
 
 define i32 @poison3(i1 %cond, i32 %x) {
 ; CHECK-LABEL: @poison3(
-; CHECK-NEXT:    [[V:%.*]] = select i1 [[COND:%.*]], i32 [[X:%.*]], i32 poison
-; CHECK-NEXT:    ret i32 [[V]]
+; CHECK-NEXT:    ret i32 [[X:%.*]]
 ;
   %v = select i1 %cond, i32 %x, i32 poison
   ret i32 %v
@@ -1066,8 +1061,7 @@ define i32 @poison3(i1 %cond, i32 %x) {
 
 define <2 x i32> @poison4(<2 x i1> %cond, <2 x i32> %x) {
 ; CHECK-LABEL: @poison4(
-; CHECK-NEXT:    [[V:%.*]] = select <2 x i1> [[COND:%.*]], <2 x i32> [[X:%.*]], <2 x i32> poison
-; CHECK-NEXT:    ret <2 x i32> [[V]]
+; CHECK-NEXT:    ret <2 x i32> [[X:%.*]]
 ;
   %v = select <2 x i1> %cond, <2 x i32> %x, <2 x i32> poison
   ret <2 x i32> %v

llvm/test/Transforms/InstSimplify/shift.ll

@@ -262,11 +262,9 @@ define i32 @poison3(i32 %x) {
   ret i32 %v
 }
 
-; TODO: these should be poison
-
 define i32 @poison4(i32 %x) {
 ; CHECK-LABEL: @poison4(
-; CHECK-NEXT:    ret i32 0
+; CHECK-NEXT:    ret i32 poison
 ;
   %v = lshr i32 poison, %x
   ret i32 %v
@@ -274,7 +272,7 @@ define i32 @poison4(i32 %x) {
 
 define i32 @poison5(i32 %x) {
 ; CHECK-LABEL: @poison5(
-; CHECK-NEXT:    ret i32 0
+; CHECK-NEXT:    ret i32 poison
 ;
   %v = ashr i32 poison, %x
   ret i32 %v
@@ -282,7 +280,7 @@ define i32 @poison5(i32 %x) {
 
 define i32 @poison6(i32 %x) {
 ; CHECK-LABEL: @poison6(
-; CHECK-NEXT:    ret i32 0
+; CHECK-NEXT:    ret i32 poison
 ;
   %v = shl i32 poison, %x
   ret i32 %v

llvm/test/Transforms/InstSimplify/sub.ll

@@ -51,11 +51,9 @@ define <2 x i32> @neg_neg_vec(<2 x i32> %A) {
   ret <2 x i32> %C
 }
 
-; TODO: these should be poison
-
 define i32 @poison1(i32 %x) {
 ; CHECK-LABEL: @poison1(
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
   %v = sub i32 %x, poison
   ret i32 %v
@@ -63,7 +61,7 @@ define i32 @poison1(i32 %x) {
 
 define i32 @poison2(i32 %x) {
 ; CHECK-LABEL: @poison2(
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
   %v = sub i32 poison, %x
   ret i32 %v