[llvm] [ValueTracking] Fix poison propagation in `matchFastFloatClamp` (PR #144215)
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llvm-commits at lists.llvm.org
Sat Jun 14 01:47:29 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-analysis
@llvm/pr-subscribers-llvm-transforms
Author: Yingwei Zheng (dtcxzyw)
<details>
<summary>Changes</summary>
https://reviews.llvm.org/D33186 converts `X < C1 ? C1 : Min(X, C2) --> Max(C1, Min(X, C2))`. However, it is problematic since `Min(X, C2)` may introduce poison (due to FMF on fcmp or select).
Closes https://github.com/llvm/llvm-project/issues/143120.
BTW, I think it is effectively dead as it is unlikely to set FMF on the second fcmp+select pair, while the first one is guaranteed not to generate poison. In addition, `*FC1 < *FC2` never holds on real-world code: https://dtcxzyw.github.io/llvm-opt-benchmark/coverage/data/zyw/opt-ci/actions-runner/_work/llvm-opt-benchmark/llvm-opt-benchmark/llvm/llvm-project/llvm/lib/Analysis/ValueTracking.cpp.html#L8187
---
Full diff: https://github.com/llvm/llvm-project/pull/144215.diff
2 Files Affected:
- (modified) llvm/lib/Analysis/ValueTracking.cpp (+2-1)
- (modified) llvm/test/Transforms/InstCombine/clamp-to-minmax.ll (+50-34)
``````````diff
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index d8c1096049dce..ca8564556d6a4 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -8181,7 +8181,8 @@ static SelectPatternResult matchFastFloatClamp(CmpInst::Predicate Pred,
RHS = FalseVal;
const APFloat *FC1;
- if (CmpRHS != TrueVal || !match(CmpRHS, m_APFloat(FC1)) || !FC1->isFinite())
+ if (CmpRHS != TrueVal || !match(CmpRHS, m_APFloat(FC1)) || !FC1->isFinite() ||
+ !isGuaranteedNotToBePoison(FalseVal))
return {SPF_UNKNOWN, SPNB_NA, false};
const APFloat *FC2;
diff --git a/llvm/test/Transforms/InstCombine/clamp-to-minmax.ll b/llvm/test/Transforms/InstCombine/clamp-to-minmax.ll
index 7f3276608c5da..ccceb315785ef 100644
--- a/llvm/test/Transforms/InstCombine/clamp-to-minmax.ll
+++ b/llvm/test/Transforms/InstCombine/clamp-to-minmax.ll
@@ -3,15 +3,15 @@
; RUN: opt < %s -passes=instcombine -use-constant-fp-for-fixed-length-splat -use-constant-int-for-fixed-length-splat -S | FileCheck %s
; (X < C1) ? C1 : MIN(X, C2)
-define float @clamp_float_fast_ordered_strict_maxmin(float %x) {
+define float @clamp_float_fast_ordered_strict_maxmin(float noundef %x) {
; CHECK-LABEL: @clamp_float_fast_ordered_strict_maxmin(
-; CHECK-NEXT: [[CMP2:%.*]] = fcmp fast olt float [[X:%.*]], 2.550000e+02
+; CHECK-NEXT: [[CMP2:%.*]] = fcmp olt float [[X:%.*]], 2.550000e+02
; CHECK-NEXT: [[MIN:%.*]] = select i1 [[CMP2]], float [[X]], float 2.550000e+02
; CHECK-NEXT: [[DOTINV:%.*]] = fcmp fast oge float [[MIN]], 1.000000e+00
; CHECK-NEXT: [[R1:%.*]] = select nnan ninf i1 [[DOTINV]], float [[MIN]], float 1.000000e+00
; CHECK-NEXT: ret float [[R1]]
;
- %cmp2 = fcmp fast olt float %x, 255.0
+ %cmp2 = fcmp olt float %x, 255.0
%min = select i1 %cmp2, float %x, float 255.0
%cmp1 = fcmp fast olt float %x, 1.0
%r = select i1 %cmp1, float 1.0, float %min
@@ -19,15 +19,15 @@ define float @clamp_float_fast_ordered_strict_maxmin(float %x) {
}
; (X <= C1) ? C1 : MIN(X, C2)
-define float @clamp_float_fast_ordered_nonstrict_maxmin(float %x) {
+define float @clamp_float_fast_ordered_nonstrict_maxmin(float noundef %x) {
; CHECK-LABEL: @clamp_float_fast_ordered_nonstrict_maxmin(
-; CHECK-NEXT: [[CMP2:%.*]] = fcmp fast olt float [[X:%.*]], 2.550000e+02
+; CHECK-NEXT: [[CMP2:%.*]] = fcmp olt float [[X:%.*]], 2.550000e+02
; CHECK-NEXT: [[MIN:%.*]] = select i1 [[CMP2]], float [[X]], float 2.550000e+02
; CHECK-NEXT: [[DOTINV:%.*]] = fcmp fast oge float [[MIN]], 1.000000e+00
; CHECK-NEXT: [[R1:%.*]] = select nnan ninf i1 [[DOTINV]], float [[MIN]], float 1.000000e+00
; CHECK-NEXT: ret float [[R1]]
;
- %cmp2 = fcmp fast olt float %x, 255.0
+ %cmp2 = fcmp olt float %x, 255.0
%min = select i1 %cmp2, float %x, float 255.0
%cmp1 = fcmp fast ole float %x, 1.0
%r = select i1 %cmp1, float 1.0, float %min
@@ -35,15 +35,15 @@ define float @clamp_float_fast_ordered_nonstrict_maxmin(float %x) {
}
; (X > C1) ? C1 : MAX(X, C2)
-define float @clamp_float_fast_ordered_strict_minmax(float %x) {
+define float @clamp_float_fast_ordered_strict_minmax(float noundef %x) {
; CHECK-LABEL: @clamp_float_fast_ordered_strict_minmax(
-; CHECK-NEXT: [[CMP2:%.*]] = fcmp fast ogt float [[X:%.*]], 1.000000e+00
+; CHECK-NEXT: [[CMP2:%.*]] = fcmp ogt float [[X:%.*]], 1.000000e+00
; CHECK-NEXT: [[MAX:%.*]] = select i1 [[CMP2]], float [[X]], float 1.000000e+00
; CHECK-NEXT: [[DOTINV:%.*]] = fcmp fast ole float [[MAX]], 2.550000e+02
; CHECK-NEXT: [[R1:%.*]] = select nnan ninf i1 [[DOTINV]], float [[MAX]], float 2.550000e+02
; CHECK-NEXT: ret float [[R1]]
;
- %cmp2 = fcmp fast ogt float %x, 1.0
+ %cmp2 = fcmp ogt float %x, 1.0
%max = select i1 %cmp2, float %x, float 1.0
%cmp1 = fcmp fast ogt float %x, 255.0
%r = select i1 %cmp1, float 255.0, float %max
@@ -51,15 +51,15 @@ define float @clamp_float_fast_ordered_strict_minmax(float %x) {
}
; (X >= C1) ? C1 : MAX(X, C2)
-define float @clamp_float_fast_ordered_nonstrict_minmax(float %x) {
+define float @clamp_float_fast_ordered_nonstrict_minmax(float noundef %x) {
; CHECK-LABEL: @clamp_float_fast_ordered_nonstrict_minmax(
-; CHECK-NEXT: [[CMP2:%.*]] = fcmp fast ogt float [[X:%.*]], 1.000000e+00
+; CHECK-NEXT: [[CMP2:%.*]] = fcmp ogt float [[X:%.*]], 1.000000e+00
; CHECK-NEXT: [[MAX:%.*]] = select i1 [[CMP2]], float [[X]], float 1.000000e+00
; CHECK-NEXT: [[DOTINV:%.*]] = fcmp fast ole float [[MAX]], 2.550000e+02
; CHECK-NEXT: [[R1:%.*]] = select nnan ninf i1 [[DOTINV]], float [[MAX]], float 2.550000e+02
; CHECK-NEXT: ret float [[R1]]
;
- %cmp2 = fcmp fast ogt float %x, 1.0
+ %cmp2 = fcmp ogt float %x, 1.0
%max = select i1 %cmp2, float %x, float 1.0
%cmp1 = fcmp fast oge float %x, 255.0
%r = select i1 %cmp1, float 255.0, float %max
@@ -70,15 +70,15 @@ define float @clamp_float_fast_ordered_nonstrict_minmax(float %x) {
; The same for unordered
; (X < C1) ? C1 : MIN(X, C2)
-define float @clamp_float_fast_unordered_strict_maxmin(float %x) {
+define float @clamp_float_fast_unordered_strict_maxmin(float noundef %x) {
; CHECK-LABEL: @clamp_float_fast_unordered_strict_maxmin(
-; CHECK-NEXT: [[CMP2_INV:%.*]] = fcmp fast oge float [[X:%.*]], 2.550000e+02
-; CHECK-NEXT: [[MIN:%.*]] = select nnan ninf i1 [[CMP2_INV]], float 2.550000e+02, float [[X]]
+; CHECK-NEXT: [[CMP2_INV:%.*]] = fcmp oge float [[X:%.*]], 2.550000e+02
+; CHECK-NEXT: [[MIN:%.*]] = select i1 [[CMP2_INV]], float 2.550000e+02, float [[X]]
; CHECK-NEXT: [[DOTINV:%.*]] = fcmp fast oge float [[MIN]], 1.000000e+00
; CHECK-NEXT: [[R:%.*]] = select nnan ninf i1 [[DOTINV]], float [[MIN]], float 1.000000e+00
; CHECK-NEXT: ret float [[R]]
;
- %cmp2 = fcmp fast ult float %x, 255.0
+ %cmp2 = fcmp ult float %x, 255.0
%min = select i1 %cmp2, float %x, float 255.0
%cmp1 = fcmp fast ult float %x, 1.0
%r = select i1 %cmp1, float 1.0, float %min
@@ -86,15 +86,15 @@ define float @clamp_float_fast_unordered_strict_maxmin(float %x) {
}
; (X <= C1) ? C1 : MIN(X, C2)
-define float @clamp_float_fast_unordered_nonstrict_maxmin(float %x) {
+define float @clamp_float_fast_unordered_nonstrict_maxmin(float noundef %x) {
; CHECK-LABEL: @clamp_float_fast_unordered_nonstrict_maxmin(
-; CHECK-NEXT: [[CMP2_INV:%.*]] = fcmp fast oge float [[X:%.*]], 2.550000e+02
-; CHECK-NEXT: [[MIN:%.*]] = select nnan ninf i1 [[CMP2_INV]], float 2.550000e+02, float [[X]]
+; CHECK-NEXT: [[CMP2_INV:%.*]] = fcmp oge float [[X:%.*]], 2.550000e+02
+; CHECK-NEXT: [[MIN:%.*]] = select i1 [[CMP2_INV]], float 2.550000e+02, float [[X]]
; CHECK-NEXT: [[DOTINV:%.*]] = fcmp fast oge float [[MIN]], 1.000000e+00
; CHECK-NEXT: [[R:%.*]] = select nnan ninf i1 [[DOTINV]], float [[MIN]], float 1.000000e+00
; CHECK-NEXT: ret float [[R]]
;
- %cmp2 = fcmp fast ult float %x, 255.0
+ %cmp2 = fcmp ult float %x, 255.0
%min = select i1 %cmp2, float %x, float 255.0
%cmp1 = fcmp fast ule float %x, 1.0
%r = select i1 %cmp1, float 1.0, float %min
@@ -102,15 +102,15 @@ define float @clamp_float_fast_unordered_nonstrict_maxmin(float %x) {
}
; (X > C1) ? C1 : MAX(X, C2)
-define float @clamp_float_fast_unordered_strict_minmax(float %x) {
+define float @clamp_float_fast_unordered_strict_minmax(float noundef %x) {
; CHECK-LABEL: @clamp_float_fast_unordered_strict_minmax(
-; CHECK-NEXT: [[CMP2_INV:%.*]] = fcmp fast ole float [[X:%.*]], 1.000000e+00
-; CHECK-NEXT: [[MAX:%.*]] = select nnan ninf i1 [[CMP2_INV]], float 1.000000e+00, float [[X]]
+; CHECK-NEXT: [[CMP2_INV:%.*]] = fcmp ole float [[X:%.*]], 1.000000e+00
+; CHECK-NEXT: [[MAX:%.*]] = select i1 [[CMP2_INV]], float 1.000000e+00, float [[X]]
; CHECK-NEXT: [[DOTINV:%.*]] = fcmp fast ole float [[MAX]], 2.550000e+02
; CHECK-NEXT: [[R:%.*]] = select nnan ninf i1 [[DOTINV]], float [[MAX]], float 2.550000e+02
; CHECK-NEXT: ret float [[R]]
;
- %cmp2 = fcmp fast ugt float %x, 1.0
+ %cmp2 = fcmp ugt float %x, 1.0
%max = select i1 %cmp2, float %x, float 1.0
%cmp1 = fcmp fast ugt float %x, 255.0
%r = select i1 %cmp1, float 255.0, float %max
@@ -118,15 +118,15 @@ define float @clamp_float_fast_unordered_strict_minmax(float %x) {
}
; (X >= C1) ? C1 : MAX(X, C2)
-define float @clamp_float_fast_unordered_nonstrict_minmax(float %x) {
+define float @clamp_float_fast_unordered_nonstrict_minmax(float noundef %x) {
; CHECK-LABEL: @clamp_float_fast_unordered_nonstrict_minmax(
-; CHECK-NEXT: [[CMP2_INV:%.*]] = fcmp fast ole float [[X:%.*]], 1.000000e+00
-; CHECK-NEXT: [[MAX:%.*]] = select nnan ninf i1 [[CMP2_INV]], float 1.000000e+00, float [[X]]
+; CHECK-NEXT: [[CMP2_INV:%.*]] = fcmp ole float [[X:%.*]], 1.000000e+00
+; CHECK-NEXT: [[MAX:%.*]] = select i1 [[CMP2_INV]], float 1.000000e+00, float [[X]]
; CHECK-NEXT: [[DOTINV:%.*]] = fcmp fast ole float [[MAX]], 2.550000e+02
; CHECK-NEXT: [[R:%.*]] = select nnan ninf i1 [[DOTINV]], float [[MAX]], float 2.550000e+02
; CHECK-NEXT: ret float [[R]]
;
- %cmp2 = fcmp fast ugt float %x, 1.0
+ %cmp2 = fcmp ugt float %x, 1.0
%max = select i1 %cmp2, float %x, float 1.0
%cmp1 = fcmp fast uge float %x, 255.0
%r = select i1 %cmp1, float 255.0, float %max
@@ -136,15 +136,15 @@ define float @clamp_float_fast_unordered_nonstrict_minmax(float %x) {
; Some more checks with fast
; (X > 1.0) ? min(x, 255.0) : 1.0
-define float @clamp_test_1(float %x) {
+define float @clamp_test_1(float noundef %x) {
; CHECK-LABEL: @clamp_test_1(
-; CHECK-NEXT: [[INNER_CMP_INV:%.*]] = fcmp fast oge float [[X:%.*]], 2.550000e+02
-; CHECK-NEXT: [[INNER_SEL:%.*]] = select nnan ninf i1 [[INNER_CMP_INV]], float 2.550000e+02, float [[X]]
-; CHECK-NEXT: [[OUTER_CMP:%.*]] = fcmp fast oge float [[INNER_SEL]], 1.000000e+00
-; CHECK-NEXT: [[R:%.*]] = select nnan ninf i1 [[OUTER_CMP]], float [[INNER_SEL]], float 1.000000e+00
+; CHECK-NEXT: [[INNER_CMP_INV:%.*]] = fcmp oge float [[X:%.*]], 2.550000e+02
+; CHECK-NEXT: [[INNER_SEL:%.*]] = select i1 [[INNER_CMP_INV]], float 2.550000e+02, float [[X]]
+; CHECK-NEXT: [[DOTINV:%.*]] = fcmp fast oge float [[INNER_SEL]], 1.000000e+00
+; CHECK-NEXT: [[R:%.*]] = select nnan ninf i1 [[DOTINV]], float [[INNER_SEL]], float 1.000000e+00
; CHECK-NEXT: ret float [[R]]
;
- %inner_cmp = fcmp fast ult float %x, 255.0
+ %inner_cmp = fcmp ult float %x, 255.0
%inner_sel = select i1 %inner_cmp, float %x, float 255.0
%outer_cmp = fcmp fast ugt float %x, 1.0
%r = select i1 %outer_cmp, float %inner_sel, float 1.0
@@ -185,6 +185,22 @@ define float @clamp_negative_same_op(float %x) {
ret float %r
}
+define float @clamp_negative_propagate_poison(float %x) {
+; CHECK-LABEL: @clamp_negative_propagate_poison(
+; CHECK-NEXT: [[CMP1:%.*]] = fcmp ninf ole float [[X:%.*]], 1.000000e+00
+; CHECK-NEXT: [[MAX:%.*]] = select i1 [[CMP1]], float 1.000000e+00, float [[X]]
+; CHECK-NEXT: [[CMP2:%.*]] = fcmp nnan ole float [[X]], 2.550000e+02
+; CHECK-NEXT: [[R1:%.*]] = select i1 [[CMP2]], float [[MAX]], float 2.550000e+02
+; CHECK-NEXT: ret float [[R1]]
+;
+ %cmp1 = fcmp ninf ole float %x, 1.000000e+00
+ %max = select i1 %cmp1, float 1.000000e+00, float %x
+ %cmp2 = fcmp nnan ole float %x, 2.550000e+02
+ %r = select i1 %cmp2, float %max, float 2.550000e+02
+ ret float %r
+}
+
+
; And now without fast.
``````````
</details>
https://github.com/llvm/llvm-project/pull/144215
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