[SLP vectorizer] Allow phi node reordering in tryToVectorizeList.

In tryToVectorizeList, under a very limited circumstance (when entered
from tryToVectorizePair), the values may be reordered (swapped) and the
SLP tree is built with the new order. This extends that to the case when
starting from phis in vectorizeChainsInBlock when there are exactly two
phis. The textual order of phi nodes shouldn't really matter. Without
this change, the loop body in the accompnaying test case is fully vectorized
when we swap the orde of the phis but not with this order. While this
doesn't solve the phi-ordering problem in a general way (for more than 2
phis), this is simple fix that piggybacks on an existing mechanism and
is useful in cases like multiplying two complex numbers.

Differential revision: https://reviews.llvm.org/D32065

llvm-svn: 300574

1 files changed, 54 insertions, 0 deletions

diff --git a/llvm/test/Transforms/SLPVectorizer/X86/reorder_phi.ll b/llvm/test/Transforms/SLPVectorizer/X86/reorder_phi.ll
new file mode 100644
index 00000000000..f7f58d7350b
--- /dev/null
+++ b/llvm/test/Transforms/SLPVectorizer/X86/reorder_phi.ll
@@ -0,0 +1,54 @@
+; RUN: opt < %s -basicaa -slp-vectorizer  -S -mtriple=x86_64-unknown -mcpu=corei7-avx | FileCheck %s
+
+%struct.complex = type { float, float }
+
+; CHECK-LABEL: void @foo
+define  void @foo (%struct.complex* %A, %struct.complex* %B, %struct.complex* %Result) {
+
+entry:
+  %0 = add i64 256, 0
+  br label %loop
+
+; CHECK-LABEL: loop
+; CHECK: [[REG0:%[0-9]+]] = phi <2 x float> {{.*}}[ [[REG1:%[0-9]+]], %loop ]
+; CHECK: [[REG2:%[0-9]+]] = load <2 x float>, <2 x float>*
+; CHECK: [[REG3:%[0-9]+]] = fmul <2 x float> [[REG2]]
+; CHECK: [[REG4:%[0-9]+]] = fmul <2 x float>
+; CHECK: fsub <2 x float> [[REG3]], [[REG4]]
+; CHECK: fadd <2 x float> [[REG3]], [[REG4]]
+; CHECK: shufflevector <2 x float>
+; CHECK: [[REG1]] = fadd <2 x float>{{.*}}[[REG0]]
+loop:
+
+  %1 = phi i64 [ 0, %entry ], [ %20, %loop ]
+  %2 = phi float [ 0.000000e+00, %entry ], [ %19, %loop ]
+  %3 = phi float [ 0.000000e+00, %entry ], [ %18, %loop ]
+  %4 = getelementptr inbounds %"struct.complex", %"struct.complex"* %A, i64 %1, i32 0
+  %5 = load float, float* %4, align 4
+  %6 = getelementptr inbounds %"struct.complex", %"struct.complex"* %A, i64 %1, i32 1
+  %7 = load float, float* %6, align 4
+  %8 = getelementptr inbounds %"struct.complex", %"struct.complex"* %B, i64 %1, i32 0
+  %9 = load float, float* %8, align 4
+  %10 = getelementptr inbounds %"struct.complex", %"struct.complex"* %B, i64 %1, i32 1
+  %11 = load float, float* %10, align 4
+  %12 = fmul float %5, %9
+  %13 = fmul float %7, %11
+  %14 = fsub float %12, %13
+  %15 = fmul float %7, %9
+  %16 = fmul float %5, %11
+  %17 = fadd float %15, %16
+  %18 = fadd float %3, %14
+  %19 = fadd float %2, %17
+  %20 = add nuw nsw i64 %1, 1
+  %21 = icmp eq i64 %20, %0
+  br i1 %21, label %exit, label %loop
+
+exit:
+  %22 = getelementptr inbounds %"struct.complex", %"struct.complex"* %Result,  i32 0, i32 0
+  store float %18, float* %22, align 4
+  %23 = getelementptr inbounds %"struct.complex", %"struct.complex"* %Result,  i32 0, i32 1
+  store float %19, float* %23, align 4
+
+  ret void
+
+}