Enhance SRoA to be more aggressive about scalarization of aggregate allocas

that have PHI or select uses of their element pointers.  This can often happen
when instcombine sinks two loads into a successor, inserting a phi or select.

With this patch, we can scalarize the alloca, but the pinned elements are not
yet promoted.  This is still a win for large aggregates where only one element
is used.  This fixes rdar://8904039 and part of rdar://7339113 (poor codegen
on stringswitch).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124070 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 78 insertions, 0 deletions

diff --git a/test/Transforms/ScalarRepl/phi-select.ll b/test/Transforms/ScalarRepl/phi-select.ll
new file mode 100644
index 0000000..06ee208
--- /dev/null
+++ b/test/Transforms/ScalarRepl/phi-select.ll
@@ -0,0 +1,78 @@
+; RUN: opt %s -scalarrepl -S | FileCheck %s
+; Test promotion of allocas that have phis and select users.
+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-darwin10.2"
+
+%struct.X = type { i32 }
+%PairTy = type {i32, i32}
+
+; CHECK: @test1
+; CHECK: %a.0 = alloca i32
+; CHECK: %b.0 = alloca i32
+define i32 @test1(i32 %x) nounwind readnone ssp {
+entry:
+  %a = alloca %struct.X, align 8                  ; <%struct.X*> [#uses=2]
+  %b = alloca %struct.X, align 8                  ; <%struct.X*> [#uses=2]
+  %0 = getelementptr inbounds %struct.X* %a, i64 0, i32 0 ; <i32*> [#uses=1]
+  store i32 1, i32* %0, align 8
+  %1 = getelementptr inbounds %struct.X* %b, i64 0, i32 0 ; <i32*> [#uses=1]
+  store i32 2, i32* %1, align 8
+  %2 = icmp eq i32 %x, 0                          ; <i1> [#uses=1]
+  %p.0 = select i1 %2, %struct.X* %b, %struct.X* %a ; <%struct.X*> [#uses=1]
+  %3 = getelementptr inbounds %struct.X* %p.0, i64 0, i32 0 ; <i32*> [#uses=1]
+  %4 = load i32* %3, align 8                      ; <i32> [#uses=1]
+  ret i32 %4
+}
+
+; CHECK: @test2
+; CHECK: %A.0 = alloca i32
+; CHECK: %A.1 = alloca i32
+define i32 @test2(i1 %c) {
+entry:
+  %A = alloca {i32, i32}
+  %B = getelementptr {i32, i32}* %A, i32 0, i32 0
+  store i32 1, i32* %B
+  br i1 %c, label %T, label %F
+T:
+  %C = getelementptr {i32, i32}* %A, i32 0, i32 1
+  store i32 2, i32* %B
+  br label %F
+F:
+  %X = phi i32* [%B, %entry], [%C, %T]
+  %Q = load i32* %X
+  ret i32 %Q
+}
+
+; CHECK: @test3
+; CHECK: %A.0 = alloca i32
+; CHECK: %A.1 = alloca i32
+; rdar://8904039
+define i32 @test3(i1 %c) {
+entry:
+  %A = alloca {i32, i32}
+  %B = getelementptr {i32, i32}* %A, i32 0, i32 0
+  store i32 1, i32* %B
+  %C = getelementptr {i32, i32}* %A, i32 0, i32 1
+  store i32 2, i32* %B
+  
+  %X = select i1 %c, i32* %B, i32* %C
+  %Q = load i32* %X
+  ret i32 %Q
+}
+
+;; We can't scalarize this, a use of the select is not an element access.
+define i64 @test4(i1 %c) {
+entry:
+  %A = alloca %PairTy
+  ; CHECK: @test4
+  ; CHECK: %A = alloca %PairTy
+  %B = getelementptr {i32, i32}* %A, i32 0, i32 0
+  store i32 1, i32* %B
+  %C = getelementptr {i32, i32}* %A, i32 0, i32 1
+  store i32 2, i32* %B
+  
+  %X = select i1 %c, i32* %B, i32* %C
+  %Y = bitcast i32* %X to i64*
+  %Q = load i64* %Y
+  ret i64 %Q
+}