[llvm] [ValueTracking] Set Ordered to true when both operands are non-NaN. (PR #143349)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/143349

When the original predicate is ordered and both operands are non-NaN, `Ordered` should be set to true. If the original one is unordered, it is also safe to be converted into an ordered predicate. This variable still matters even if both operands are non-NaN because FMF only applies to select, not fcmp.

Closes https://github.com/llvm/llvm-project/issues/143123.


>From 23aebb7c81ac0591a6ec8d3ab928df4c55061886 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 9 Jun 2025 13:48:12 +0800
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests. NFC.

---
 .../Transforms/InstCombine/fcmp-select.ll     | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/llvm/test/Transforms/InstCombine/fcmp-select.ll b/llvm/test/Transforms/InstCombine/fcmp-select.ll
index 053b233cb5f04..705afee255d18 100644
--- a/llvm/test/Transforms/InstCombine/fcmp-select.ll
+++ b/llvm/test/Transforms/InstCombine/fcmp-select.ll
@@ -270,12 +270,25 @@ define i1 @test_fcmp_select_var_const_unordered(double %x, double %y) {
 }
 
 define i1 @test_fcmp_ord_select_fcmp_oeq_var_const(double %x) {
-; CHECK-LABEL:    @test_fcmp_ord_select_fcmp_oeq_var_const(
-; CHECK-NEXT:     [[CMP1:%.*]] = fcmp oeq double [[X:%.*]], 1.000000e+00
-; CHECK-NEXT:     ret i1 [[CMP1]]
+; CHECK-LABEL: @test_fcmp_ord_select_fcmp_oeq_var_const(
+; CHECK-NEXT:    [[TMP1:%.*]] = fcmp oeq double [[X:%.*]], 1.000000e+00
+; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   %cmp1 = fcmp ord double %x, 0.000000e+00
   %sel = select i1 %cmp1, double %x, double 0.000000e+00
   %cmp2 = fcmp oeq double %sel, 1.000000e+00
   ret i1 %cmp2
 }
+
+; Make sure that we recognize the SPF correctly.
+
+define float @test_select_nnan_nsz_fcmp_olt(float %x) {
+; CHECK-LABEL: @test_select_nnan_nsz_fcmp_olt(
+; CHECK-NEXT:    [[DOTINV:%.*]] = fcmp oge float [[X:%.*]], 0.000000e+00
+; CHECK-NEXT:    [[SEL1:%.*]] = select i1 [[DOTINV]], float -0.000000e+00, float [[X]]
+; CHECK-NEXT:    ret float [[SEL1]]
+;
+  %cmp = fcmp olt float %x, 0.000000e+00
+  %sel = select nnan nsz i1 %cmp, float %x, float -0.000000e+00
+  ret float %sel
+}

>From ef884b52ec771248a26a82b0284bfb2dea928cdf Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 9 Jun 2025 13:49:32 +0800
Subject: [PATCH 2/2] [ValueTracking] Set Ordered to true when both operands
 are non-NaN.

---
 llvm/lib/Analysis/ValueTracking.cpp             | 2 ++
 llvm/test/Transforms/InstCombine/fcmp-select.ll | 4 ++--
 llvm/unittests/Analysis/ValueTrackingTest.cpp   | 2 +-
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index d6bb852e208f9..e65e34cda95ac 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -8660,6 +8660,8 @@ static SelectPatternResult matchSelectPattern(CmpInst::Predicate Pred,
     if (LHSSafe && RHSSafe) {
       // Both operands are known non-NaN.
       NaNBehavior = SPNB_RETURNS_ANY;
+      // It is always safe to convert the comparison to an ordered one.
+      Ordered = true;
     } else if (CmpInst::isOrdered(Pred)) {
       // An ordered comparison will return false when given a NaN, so it
       // returns the RHS.
diff --git a/llvm/test/Transforms/InstCombine/fcmp-select.ll b/llvm/test/Transforms/InstCombine/fcmp-select.ll
index 705afee255d18..9434f6da0b9b3 100644
--- a/llvm/test/Transforms/InstCombine/fcmp-select.ll
+++ b/llvm/test/Transforms/InstCombine/fcmp-select.ll
@@ -284,8 +284,8 @@ define i1 @test_fcmp_ord_select_fcmp_oeq_var_const(double %x) {
 
 define float @test_select_nnan_nsz_fcmp_olt(float %x) {
 ; CHECK-LABEL: @test_select_nnan_nsz_fcmp_olt(
-; CHECK-NEXT:    [[DOTINV:%.*]] = fcmp oge float [[X:%.*]], 0.000000e+00
-; CHECK-NEXT:    [[SEL1:%.*]] = select i1 [[DOTINV]], float -0.000000e+00, float [[X]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fcmp olt float [[X:%.*]], -0.000000e+00
+; CHECK-NEXT:    [[SEL1:%.*]] = select i1 [[TMP1]], float [[X]], float -0.000000e+00
 ; CHECK-NEXT:    ret float [[SEL1]]
 ;
   %cmp = fcmp olt float %x, 0.000000e+00
diff --git a/llvm/unittests/Analysis/ValueTrackingTest.cpp b/llvm/unittests/Analysis/ValueTrackingTest.cpp
index e23005b60891d..faf72bb17880b 100644
--- a/llvm/unittests/Analysis/ValueTrackingTest.cpp
+++ b/llvm/unittests/Analysis/ValueTrackingTest.cpp
@@ -187,7 +187,7 @@ TEST_F(MatchSelectPatternTest, FastFMin) {
       "  %A = select i1 %1, float %a, float 5.0\n"
       "  ret float %A\n"
       "}\n");
-  expectPattern({SPF_FMINNUM, SPNB_RETURNS_ANY, false});
+  expectPattern({SPF_FMINNUM, SPNB_RETURNS_ANY, true});
 }
 
 TEST_F(MatchSelectPatternTest, FMinConstantZero) {