[llvm] c8ed784 - [InstCombine] fold freeze of partial undef/poison vector constants
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 26 11:16:19 PDT 2022
Author: Sanjay Patel
Date: 2022-04-26T14:16:11-04:00
New Revision: c8ed784ee69a7dbdf4b33e85229457ffad309cf2
URL: https://github.com/llvm/llvm-project/commit/c8ed784ee69a7dbdf4b33e85229457ffad309cf2
DIFF: https://github.com/llvm/llvm-project/commit/c8ed784ee69a7dbdf4b33e85229457ffad309cf2.diff
LOG: [InstCombine] fold freeze of partial undef/poison vector constants
We can always replace the undef elements in a vector constant
with regular constants to get rid of the freeze:
https://alive2.llvm.org/ce/z/nfRb4F
The select diffs show that we might do better by adjusting the
logic for a frozen select condition. We may also want to refine
the vector constant replacement to consider forming a splat.
Differential Revision: https://reviews.llvm.org/D123962
Added:
Modified:
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
llvm/test/Transforms/InstCombine/freeze-phi.ll
llvm/test/Transforms/InstCombine/freeze.ll
llvm/test/Transforms/InstCombine/select.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index b1f2e8bbc85ee..e8bd680434194 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3778,29 +3778,45 @@ Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
if (Value *NI = pushFreezeToPreventPoisonFromPropagating(I))
return replaceInstUsesWith(I, NI);
- if (match(Op0, m_Undef())) {
- // If I is freeze(undef), check its uses and fold it to a fixed constant.
- // - or: pick -1
- // - select's condition: if the true value is constant, choose it by making
- // the condition true.
- // - default: pick 0
+ // If I is freeze(undef), check its uses and fold it to a fixed constant.
+ // - or: pick -1
+ // - select's condition: if the true value is constant, choose it by making
+ // the condition true.
+ // - default: pick 0
+ //
+ // Note that this transform is intentionally done here rather than
+ // via an analysis in InstSimplify or at individual user sites. That is
+ // because we must produce the same value for all uses of the freeze -
+ // it's the reason "freeze" exists!
+ //
+ // TODO: This could use getBinopAbsorber() / getBinopIdentity() to avoid
+ // duplicating logic for binops at least.
+ auto getUndefReplacement = [&I](Type *Ty) {
Constant *BestValue = nullptr;
- Constant *NullValue = Constant::getNullValue(I.getType());
+ Constant *NullValue = Constant::getNullValue(Ty);
for (const auto *U : I.users()) {
Constant *C = NullValue;
-
if (match(U, m_Or(m_Value(), m_Value())))
- C = ConstantInt::getAllOnesValue(I.getType());
+ C = ConstantInt::getAllOnesValue(Ty);
else if (match(U, m_Select(m_Specific(&I), m_Constant(), m_Value())))
- C = ConstantInt::getTrue(I.getType());
+ C = ConstantInt::getTrue(Ty);
if (!BestValue)
BestValue = C;
else if (BestValue != C)
BestValue = NullValue;
}
+ assert(BestValue && "Must have at least one use");
+ return BestValue;
+ };
+
+ if (match(Op0, m_Undef()))
+ return replaceInstUsesWith(I, getUndefReplacement(I.getType()));
- return replaceInstUsesWith(I, BestValue);
+ Constant *C;
+ if (match(Op0, m_Constant(C)) && C->containsUndefOrPoisonElement()) {
+ Constant *ReplaceC = getUndefReplacement(I.getType()->getScalarType());
+ return replaceInstUsesWith(I, Constant::replaceUndefsWith(C, ReplaceC));
}
// Replace all dominated uses of Op to freeze(Op).
diff --git a/llvm/test/Transforms/InstCombine/freeze-phi.ll b/llvm/test/Transforms/InstCombine/freeze-phi.ll
index 87e4d324114f8..207179bb2c098 100644
--- a/llvm/test/Transforms/InstCombine/freeze-phi.ll
+++ b/llvm/test/Transforms/InstCombine/freeze-phi.ll
@@ -51,10 +51,9 @@ define <2 x i32> @vec_undef(i1 %cond) {
; CHECK: A:
; CHECK-NEXT: br label [[C:%.*]]
; CHECK: B:
-; CHECK-NEXT: [[PHI_FR:%.*]] = freeze <2 x i32> <i32 2, i32 undef>
; CHECK-NEXT: br label [[C]]
; CHECK: C:
-; CHECK-NEXT: [[Y:%.*]] = phi <2 x i32> [ <i32 0, i32 1>, [[A]] ], [ [[PHI_FR]], [[B]] ]
+; CHECK-NEXT: [[Y:%.*]] = phi <2 x i32> [ <i32 0, i32 1>, [[A]] ], [ <i32 2, i32 0>, [[B]] ]
; CHECK-NEXT: ret <2 x i32> [[Y]]
;
br i1 %cond, label %A, label %B
diff --git a/llvm/test/Transforms/InstCombine/freeze.ll b/llvm/test/Transforms/InstCombine/freeze.ll
index 3fee57ac0c022..3b85b0bd80b5b 100644
--- a/llvm/test/Transforms/InstCombine/freeze.ll
+++ b/llvm/test/Transforms/InstCombine/freeze.ll
@@ -89,8 +89,7 @@ define void @or_select_multipleuses_logical(i32 %x, i1 %y) {
define <3 x i4> @partial_undef_vec() {
; CHECK-LABEL: @partial_undef_vec(
-; CHECK-NEXT: [[F:%.*]] = freeze <3 x i4> <i4 poison, i4 1, i4 undef>
-; CHECK-NEXT: ret <3 x i4> [[F]]
+; CHECK-NEXT: ret <3 x i4> <i4 0, i4 1, i4 0>
;
%f = freeze <3 x i4> <i4 poison, i4 1, i4 undef>
ret <3 x i4> %f
diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index e68c8e5432605..4f90b14f1b260 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -2633,9 +2633,7 @@ define <2 x i8> @cond_freeze_constant_true_val_vec(<2 x i8> %x) {
define <2 x i8> @partial_cond_freeze_constant_true_val_vec(<2 x i8> %x) {
; CHECK-LABEL: @partial_cond_freeze_constant_true_val_vec(
-; CHECK-NEXT: [[COND_FR:%.*]] = freeze <2 x i1> <i1 true, i1 undef>
-; CHECK-NEXT: [[S:%.*]] = select <2 x i1> [[COND_FR]], <2 x i8> <i8 1, i8 2>, <2 x i8> [[X:%.*]]
-; CHECK-NEXT: ret <2 x i8> [[S]]
+; CHECK-NEXT: ret <2 x i8> <i8 1, i8 2>
;
%cond.fr = freeze <2 x i1> <i1 true, i1 undef>
%s = select <2 x i1> %cond.fr, <2 x i8> <i8 1, i8 2>, <2 x i8> %x
@@ -2644,9 +2642,8 @@ define <2 x i8> @partial_cond_freeze_constant_true_val_vec(<2 x i8> %x) {
define <2 x i8> @partial_cond_freeze_constant_false_val_vec(<2 x i8> %x) {
; CHECK-LABEL: @partial_cond_freeze_constant_false_val_vec(
-; CHECK-NEXT: [[COND_FR:%.*]] = freeze <2 x i1> <i1 true, i1 undef>
-; CHECK-NEXT: [[S:%.*]] = select <2 x i1> [[COND_FR]], <2 x i8> [[X:%.*]], <2 x i8> <i8 1, i8 2>
-; CHECK-NEXT: ret <2 x i8> [[S]]
+; CHECK-NEXT: [[S1:%.*]] = insertelement <2 x i8> [[X:%.*]], i8 2, i64 1
+; CHECK-NEXT: ret <2 x i8> [[S1]]
;
%cond.fr = freeze <2 x i1> <i1 true, i1 undef>
%s = select <2 x i1> %cond.fr, <2 x i8> %x, <2 x i8> <i8 1, i8 2>
@@ -2655,9 +2652,7 @@ define <2 x i8> @partial_cond_freeze_constant_false_val_vec(<2 x i8> %x) {
define <2 x i8> @partial_cond_freeze_both_arms_constant_vec() {
; CHECK-LABEL: @partial_cond_freeze_both_arms_constant_vec(
-; CHECK-NEXT: [[COND_FR:%.*]] = freeze <2 x i1> <i1 false, i1 undef>
-; CHECK-NEXT: [[S:%.*]] = select <2 x i1> [[COND_FR]], <2 x i8> <i8 1, i8 2>, <2 x i8> <i8 42, i8 43>
-; CHECK-NEXT: ret <2 x i8> [[S]]
+; CHECK-NEXT: ret <2 x i8> <i8 42, i8 2>
;
%cond.fr = freeze <2 x i1> <i1 false, i1 undef>
%s = select <2 x i1> %cond.fr, <2 x i8> <i8 1, i8 2>, <2 x i8> <i8 42, i8 43>
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