[PATCH] D25493: [PPCMIPeephole] Fix splat elimination

[Tim Shen via llvm-commits]

timshen updated this revision to Diff 74313.
timshen added a comment.

Updated to build a new instruction instead of mutating the original one.


https://reviews.llvm.org/D25493

Files:
  llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
  llvm/test/CodeGen/PowerPC/pr30663.ll


Index: llvm/test/CodeGen/PowerPC/pr30663.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/PowerPC/pr30663.ll
@@ -0,0 +1,24 @@
+; RUN: llc -O1 < %s | FileCheck %s
+target triple = "powerpc64le-linux-gnu"
+
+; The second xxspltw should be eliminated.
+; CHECK: xxspltw
+; CHECK-NOT: xxspltw
+define void @Test() {
+bb4:
+  %tmp = load <4 x i8>, <4 x i8>* undef
+  %tmp8 = bitcast <4 x i8> %tmp to float
+  %tmp18 = fmul float %tmp8, undef
+  %tmp19 = fsub float 0.000000e+00, %tmp18
+  store float %tmp19, float* undef
+  %tmp22 = shufflevector <4 x i8> %tmp, <4 x i8> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
+  %tmp23 = bitcast <16 x i8> %tmp22 to <4 x float>
+  %tmp25 = tail call <4 x float> @llvm.fma.v4f32(<4 x float> undef, <4 x float> %tmp23, <4 x float> undef)
+  %tmp26 = fsub <4 x float> zeroinitializer, %tmp25
+  %tmp27 = bitcast <4 x float> %tmp26 to <4 x i32>
+  tail call void @llvm.ppc.altivec.stvx(<4 x i32> %tmp27, i8* undef)
+  ret void
+}
+
+declare void @llvm.ppc.altivec.stvx(<4 x i32>, i8*)
+declare <4 x float> @llvm.fma.v4f32(<4 x float>, <4 x float>, <4 x float>)
Index: llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
+++ llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
@@ -201,11 +201,13 @@
         // Splat fed by another splat - switch the output of the first
         // and remove the second.
         if (SameOpcode) {
-          DefMI->getOperand(0).setReg(MI.getOperand(0).getReg());
+          DEBUG(dbgs() << "Changing redundant splat to a copy: ");
+          DEBUG(MI.dump());
+          BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(PPC::COPY),
+                  MI.getOperand(0).getReg())
+              .addOperand(MI.getOperand(OpNo));
           ToErase = &MI;
           Simplified = true;
-          DEBUG(dbgs() << "Removing redundant splat: ");
-          DEBUG(MI.dump());
         }
         // Splat fed by a shift. Usually when we align value to splat into
         // vector element zero.


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