[llvm-branch-commits] [llvm] 121baba - [SelectionDAG] Don't remove unused negated constant immediately

[Hans Wennborg via llvm-branch-commits]

Author: Qiu Chaofan
Date: 2020-10-06T16:04:19+02:00
New Revision: 121babae56e9f08acedf3d6d44757e35556d0a37

URL: https://github.com/llvm/llvm-project/commit/121babae56e9f08acedf3d6d44757e35556d0a37
DIFF: https://github.com/llvm/llvm-project/commit/121babae56e9f08acedf3d6d44757e35556d0a37.diff

LOG: [SelectionDAG] Don't remove unused negated constant immediately

This reverts partial of a2fb5446 (actually, 2508ef01) about removing
negated FP constant immediately if it has no uses. However, as discussed
in bug 47517, there're cases when NegX is folded into constant from
other places while NegY is removed by that line of code and NegX is
equal to NegY. In these cases, NegX is deleted before used and crash
happens. So revert the code and add necessary test case.

(cherry picked from commit b326d4ff946d2061a566a3fcce9f33b484759fe0)

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
    llvm/test/CodeGen/X86/pr47517.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 64af293caf9ea..8b3e6189a07f8 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -5751,10 +5751,8 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
 
     // If we already have the use of the negated floating constant, it is free
     // to negate it even it has multiple uses.
-    if (!Op.hasOneUse() && CFP.use_empty()) {
-      RemoveDeadNode(CFP);
+    if (!Op.hasOneUse() && CFP.use_empty())
       break;
-    }
     Cost = NegatibleCost::Neutral;
     return CFP;
   }

diff  --git a/llvm/test/CodeGen/X86/pr47517.ll b/llvm/test/CodeGen/X86/pr47517.ll
index 5672fbc69a41d..afc27b49ab2a4 100644
--- a/llvm/test/CodeGen/X86/pr47517.ll
+++ b/llvm/test/CodeGen/X86/pr47517.ll
@@ -26,3 +26,16 @@ entry:
   %fmul6 = fmul fast float %fmul3, %fadd4
   ret float %fmul6
 }
+
+; To ensure negated result will not be removed when NegX=NegY and
+; NegX is needed
+define float @test2(float %x, float %y) {
+  %add = fadd fast float %x, 750.0
+  %sub = fsub fast float %x, %add
+  %mul = fmul fast float %sub, %sub
+  %mul2 = fmul fast float %mul, %sub
+  %add2 = fadd fast float %mul2, 1.0
+  %add3 = fadd fast float %mul2, %add2
+  %mul3 = fmul fast float %y, %add3
+  ret float %mul3
+}