When a set of bitmask operations, typically from a bitfield initialization, only modifies the low bytes of a value,

we can narrow the store to only over-write the affected bytes.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111568 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 21 insertions, 0 deletions

diff --git a/test/Transforms/InstCombine/2010-08-19-StoreNarrowing.ll b/test/Transforms/InstCombine/2010-08-19-StoreNarrowing.ll
new file mode 100644
index 0000000000..d4d528943f
--- /dev/null
+++ b/test/Transforms/InstCombine/2010-08-19-StoreNarrowing.ll
@@ -0,0 +1,21 @@
+; RUN: opt -S -instcombine %s | not grep and
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-apple-darwin10.0.0"
+
+%class.A = type { i8, [3 x i8] }
+
+define void @_ZN1AC2Ev(%class.A* %this) nounwind ssp align 2 {
+entry:
+  %0 = bitcast %class.A* %this to i32*            ; <i32*> [#uses=5]
+  %1 = load i32* %0, align 4                      ; <i32> [#uses=1]
+  %2 = and i32 %1, -8                             ; <i32> [#uses=2]
+  store i32 %2, i32* %0, align 4
+  %3 = and i32 %2, -57                            ; <i32> [#uses=1]
+  %4 = or i32 %3, 8                               ; <i32> [#uses=2]
+  store i32 %4, i32* %0, align 4
+  %5 = and i32 %4, -65                            ; <i32> [#uses=2]
+  store i32 %5, i32* %0, align 4
+  %6 = and i32 %5, -129                           ; <i32> [#uses=1]
+  store i32 %6, i32* %0, align 4
+  ret void
+}