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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

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.


---
Full diff: https://github.com/llvm/llvm-project/pull/143349.diff


3 Files Affected:

- (modified) llvm/lib/Analysis/ValueTracking.cpp (+2) 
- (modified) llvm/test/Transforms/InstCombine/fcmp-select.ll (+16-3) 
- (modified) llvm/unittests/Analysis/ValueTrackingTest.cpp (+1-1) 


``````````diff
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 053b233cb5f04..9434f6da0b9b3 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:    [[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
+  %sel = select nnan nsz i1 %cmp, float %x, float -0.000000e+00
+  ret float %sel
+}
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) {

``````````

</details>


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