Fix Sub-register Rewriting in Aggressive Anti-Dependence Breaker

Previously, HandleLastUse would delete RegRef information for sub-registers
if they were dead even if their corresponding super-register were still live.

If the super-register were later renamed, then the definitions of the
sub-register would not be updated appropriately. This patch alters the
behavior so that RegInfo information for sub-registers is only deleted when
the sub-register and super-register are both dead.

This resolves PR26775. This is the mirror image of Hal's r227311 commit.

Author: Tom Jablin (tjablin)
Reviewers: kbarton uweigand nemanjai hfinkel

http://reviews.llvm.org/D18448

llvm-svn: 265097

1 files changed, 24 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/PowerPC/aggressive-anti-dep-breaker-subreg.ll b/llvm/test/CodeGen/PowerPC/aggressive-anti-dep-breaker-subreg.ll
new file mode 100644
index 00000000000..c57588668d8
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/aggressive-anti-dep-breaker-subreg.ll
@@ -0,0 +1,24 @@
+; RUN: llc %s -mtriple=powerpc64-unknown-linux-gnu -O2 -o - -optimize-regalloc=false -regalloc=fast | FileCheck %s
+
+declare void @func(i8*, i64, i64)
+
+define void @test(i8* %context, i32** %elementArrayPtr, i32 %value) {
+entry:
+  %cmp = icmp eq i32 %value, 0
+  br i1 %cmp, label %lreturn, label %lnext
+
+lnext:
+  %elementArray = load i32*, i32** %elementArrayPtr, align 8
+; CHECK: lwz [[LDREG:[0-9]+]], 124(1)                   # 4-byte Folded Reload
+; CHECK: # implicit-def: %X[[TEMPREG:[0-9]+]]
+  %element = load i32, i32* %elementArray, align 4
+; CHECK: mr [[TEMPREG]], [[LDREG]]
+; CHECK: clrldi   4, [[TEMPREG]], 32
+  %element.ext = zext i32 %element to i64
+  %value.ext = zext i32 %value to i64
+  call void @func(i8* %context, i64 %value.ext, i64 %element.ext)
+  br label %lreturn
+
+lreturn:
+  ret void
+}