Reapply [LSR] Create fewer redundant instructions.

Summary:
Fix LSRInstance::HoistInsertPosition() to check the original insert
position block first for a canonical insertion point that is dominated
by all inputs.  This leads to SCEV being able to reuse more instructions
since it currently tracks the instructions it creates for reuse by
keeping a table of <Value, insert point> pairs.

Originally reviewed in http://reviews.llvm.org/D18001

Reviewers: atrick

Subscribers: llvm-commits, mzolotukhin, mcrosier

Differential Revision: http://reviews.llvm.org/D18480

llvm-svn: 271929

1 files changed, 34 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopStrengthReduce/AArch64/lsr-reuse.ll b/llvm/test/Transforms/LoopStrengthReduce/AArch64/lsr-reuse.ll
new file mode 100644
index 00000000000..a2dfe81b108
--- /dev/null
+++ b/llvm/test/Transforms/LoopStrengthReduce/AArch64/lsr-reuse.ll
@@ -0,0 +1,34 @@
+; RUN: llc -mtriple=arm64-unknown-unknown -print-lsr-output < %s 2>&1 | FileCheck %s
+
+declare void @foo(i64)
+
+; Verify that redundant adds aren't inserted by LSR.
+; CHECK-LABEL: @bar(
+define void @bar(double* %A) {
+entry:
+  br label %while.cond
+
+while.cond:
+; CHECK-LABEL: while.cond:
+; CHECK: add i64 %lsr.iv, 1
+; CHECK-NOT: add i64 %lsr.iv, 1
+; CHECK-LABEL: land.rhs:
+  %indvars.iv28 = phi i64 [ %indvars.iv.next29, %land.rhs ], [ 50, %entry ]
+  %cmp = icmp sgt i64 %indvars.iv28, 0
+  br i1 %cmp, label %land.rhs, label %while.end
+
+land.rhs:
+  %indvars.iv.next29 = add nsw i64 %indvars.iv28, -1
+  %arrayidx = getelementptr inbounds double, double* %A, i64 %indvars.iv.next29
+  %Aload = load double, double* %arrayidx, align 8
+  %cmp1 = fcmp oeq double %Aload, 0.000000e+00
+  br i1 %cmp1, label %while.cond, label %if.end
+
+while.end:
+  %indvars.iv28.lcssa = phi i64 [ %indvars.iv28, %while.cond ]
+  tail call void @foo(i64 %indvars.iv28.lcssa)
+  br label %if.end
+
+if.end:
+  ret void
+}