[llvm] 4e4db6f - Revert "[SelectionDAG] Use logic right shift to avoid loop hang"

[Shengchen Kan via llvm-commits]

Author: Shengchen Kan
Date: 2023-05-02T13:14:47+08:00
New Revision: 4e4db6f6c6ce13855d03f1e7a00296e49fed0765

URL: https://github.com/llvm/llvm-project/commit/4e4db6f6c6ce13855d03f1e7a00296e49fed0765
DIFF: https://github.com/llvm/llvm-project/commit/4e4db6f6c6ce13855d03f1e7a00296e49fed0765.diff

LOG: Revert "[SelectionDAG] Use logic right shift to avoid loop hang"

This reverts commit b73229e55543b4ba2b293adcb8b7d6025f01f7d9.

It caused LIT failure on non-X86 targets.

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

Removed: 
    llvm/test/CodeGen/X86/powi-negative-imm.ll


################################################################################
diff  --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 614de88663ec1..37976337a5fd8 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5459,6 +5459,9 @@ static SDValue ExpandPowI(const SDLoc &DL, SDValue LHS, SDValue RHS,
 
     if (DAG.getTargetLoweringInfo().isBeneficialToExpandPowI(
             Val, DAG.shouldOptForSize())) {
+      // Get the exponent as a positive value.
+      if (Val < 0)
+        Val = -Val;
       // We use the simple binary decomposition method to generate the multiply
       // sequence.  There are more optimal ways to do this (for example,
       // powi(x,15) generates one more multiply than it should), but this has
@@ -5478,8 +5481,7 @@ static SDValue ExpandPowI(const SDLoc &DL, SDValue LHS, SDValue RHS,
 
         CurSquare = DAG.getNode(ISD::FMUL, DL, CurSquare.getValueType(),
                                 CurSquare, CurSquare);
-        // Use logic right shift
-        Val = int(unsigned(Val) >> 1);
+        Val >>= 1;
       }
 
       // If the original was negative, invert the result, producing 1/(x*x*x).

diff  --git a/llvm/test/CodeGen/X86/powi-negative-imm.ll b/llvm/test/CodeGen/X86/powi-negative-imm.ll
deleted file mode 100644
index e3e3f51edcbf6..0000000000000
--- a/llvm/test/CodeGen/X86/powi-negative-imm.ll
+++ /dev/null
@@ -1,21 +0,0 @@
-; RUN: llc -mtriple=x86_64-unknown-unknown < %s | FileCheck %s
-
-define void @test_powi(ptr %p) nounwind {
-; CHECK-LABEL: powi:
-; CHECK:             pushq %rax
-; CHECK-NEXT:        movss {{.*#+}} xmm1 = mem[0],zero,zero,zero
-; CHECK-COUNT-31:    mulss %xmm1, %xmm1
-; CHECK-NEXT:        movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
-; CHECK-NEXT:        divss %xmm1, %xmm0
-; CHECK-NEXT:        callq foo at PLT
-; CHECK-NEXT:        popq %rax
-; CHECK-NEXT:        retq
-bb:
-  %load = load float, ptr %p, align 4
-  %call1 = call contract float @llvm.powi.f32.i32(float %load, i32 -2147483648)
-  %call2 = call i1 @foo(float %call1)
-  ret void
-}
-
-declare zeroext i1 @foo(float)
-declare float @llvm.powi.f32.i32(float, i32)