[llvm] 2981a94 - [EarlyCSE][ConstantFolding] do not constant fold atan2(+/-0.0, +/-0.0), part 2

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2022-08-20T10:16:06-04:00
New Revision: 2981a9490277a7920936d287c9703f0f7edef84b

URL: https://github.com/llvm/llvm-project/commit/2981a9490277a7920936d287c9703f0f7edef84b
DIFF: https://github.com/llvm/llvm-project/commit/2981a9490277a7920936d287c9703f0f7edef84b.diff

LOG: [EarlyCSE][ConstantFolding] do not constant fold atan2(+/-0.0, +/-0.0), part 2

Follow-up to 7f1262a322c0d80f3. That patch avoided removing the
call, but it still allowed the constant-folded result. This
makes the behavior consistent with 1-arg libm folding: if the
call potentially raises an exception, then we just bail out.

It seems likely that there are other corner-cases like this,
but the tests are incomplete, so we have lived with these
discrepancies for a long time. This was untested before the
the constant folding was expanded in D127964.

Added: 
    

Modified: 
    llvm/lib/Analysis/ConstantFolding.cpp
    llvm/test/Transforms/EarlyCSE/atan.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 8ed291778da62..9187d49ca7a5a 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -2569,6 +2569,11 @@ static Constant *ConstantFoldScalarCall2(StringRef Name,
         break;
       case LibFunc_atan2:
       case LibFunc_atan2f:
+        // atan2(+/-0.0, +/-0.0) is known to raise an exception on some libm
+        // (Solaris), so we do not assume a known result for that.
+        if (Op1V.isZero() && Op2V.isZero())
+          return nullptr;
+        [[fallthrough]];
       case LibFunc_atan2_finite:
       case LibFunc_atan2f_finite:
         if (TLI->has(Func))

diff  --git a/llvm/test/Transforms/EarlyCSE/atan.ll b/llvm/test/Transforms/EarlyCSE/atan.ll
index adb6ff7f5c03e..e665e0c9e54d9 100644
--- a/llvm/test/Transforms/EarlyCSE/atan.ll
+++ b/llvm/test/Transforms/EarlyCSE/atan.ll
@@ -55,7 +55,7 @@ define x86_fp80 @atanl_x86(x86_fp80 %x) {
 define float @callatan2_00() {
 ; CHECK-LABEL: @callatan2_00(
 ; CHECK-NEXT:    [[CALL:%.*]] = call float @atan2f(float 0.000000e+00, float 0.000000e+00)
-; CHECK-NEXT:    ret float 0.000000e+00
+; CHECK-NEXT:    ret float [[CALL]]
 ;
   %call = call float @atan2f(float 0.0, float 0.0)
   ret float %call
@@ -66,7 +66,7 @@ define float @callatan2_00() {
 define float @callatan2_n00() {
 ; CHECK-LABEL: @callatan2_n00(
 ; CHECK-NEXT:    [[CALL:%.*]] = call float @atan2f(float -0.000000e+00, float 0.000000e+00)
-; CHECK-NEXT:    ret float -0.000000e+00
+; CHECK-NEXT:    ret float [[CALL]]
 ;
   %call = call float @atan2f(float -0.0, float 0.0)
   ret float %call
@@ -77,7 +77,7 @@ define float @callatan2_n00() {
 define float @callatan2_0n0() {
 ; CHECK-LABEL: @callatan2_0n0(
 ; CHECK-NEXT:    [[CALL:%.*]] = call float @atan2f(float 0.000000e+00, float -0.000000e+00)
-; CHECK-NEXT:    ret float 0x400921FB60000000
+; CHECK-NEXT:    ret float [[CALL]]
 ;
   %call = call float @atan2f(float 0.0, float -0.0)
   ret float %call
@@ -88,7 +88,7 @@ define float @callatan2_0n0() {
 define float @callatan2_n0n0() {
 ; CHECK-LABEL: @callatan2_n0n0(
 ; CHECK-NEXT:    [[CALL:%.*]] = call float @atan2f(float -0.000000e+00, float -0.000000e+00)
-; CHECK-NEXT:    ret float 0xC00921FB60000000
+; CHECK-NEXT:    ret float [[CALL]]
 ;
   %call = call float @atan2f(float -0.0, float -0.0)
   ret float %call