Add an instcombine to clean up a common pattern produced

by the SRoA "promote to large integer" code, eliminating
some type conversions like this:

   %94 = zext i16 %93 to i32                       ; <i32> [#uses=2]
   %96 = lshr i32 %94, 8                           ; <i32> [#uses=1]
   %101 = trunc i32 %96 to i8                      ; <i8> [#uses=1]

This also unblocks other xforms from happening, now clang is able to compile:

struct S { float A, B, C, D; };
float foo(struct S A) { return A.A + A.B+A.C+A.D; }

into:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	pshufd	$1, %xmm0, %xmm2
	addss	%xmm0, %xmm2
	movdqa	%xmm1, %xmm3
	addss	%xmm2, %xmm3
	pshufd	$1, %xmm1, %xmm0
	addss	%xmm3, %xmm0
	ret

on x86-64, instead of:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	movd	%xmm0, %rax
	shrq	$32, %rax
	movd	%eax, %xmm2
	addss	%xmm0, %xmm2
	movapd	%xmm1, %xmm3
	addss	%xmm2, %xmm3
	movd	%xmm1, %rax
	shrq	$32, %rax
	movd	%eax, %xmm0
	addss	%xmm3, %xmm0
	ret

This seems pretty close to optimal to me, at least without
using horizontal adds.  This also triggers in lots of other
code, including SPEC.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112278 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 32 insertions, 0 deletions

diff --git a/test/Transforms/InstCombine/trunc.ll b/test/Transforms/InstCombine/trunc.ll
index 2fa5d37b0f..5cb3474667 100644
--- a/test/Transforms/InstCombine/trunc.ll
+++ b/test/Transforms/InstCombine/trunc.ll
@@ -48,3 +48,35 @@ define i64 @test4(i64 %a) {
 ; CHECK: %d = xor i64 {{.*}}, 8
 ; CHECK: ret i64 %d
 }
+
+define i32 @test5(i32 %A) {
+  %B = zext i32 %A to i128
+  %C = lshr i128 %B, 16
+  %D = trunc i128 %C to i32
+  ret i32 %D
+; CHECK: @test5
+; CHECK: %C = lshr i32 %A, 16
+; CHECK: ret i32 %C
+}
+
+define i32 @test6(i64 %A) {
+  %B = zext i64 %A to i128
+  %C = lshr i128 %B, 32
+  %D = trunc i128 %C to i32
+  ret i32 %D
+; CHECK: @test6
+; CHECK: %C = lshr i64 %A, 32
+; CHECK: %D = trunc i64 %C to i32
+; CHECK: ret i32 %D
+}
+
+define i92 @test7(i64 %A) {
+  %B = zext i64 %A to i128
+  %C = lshr i128 %B, 32
+  %D = trunc i128 %C to i92
+  ret i92 %D
+; CHECK: @test7
+; CHECK: %C = lshr i64 %A, 32
+; CHECK: %D = zext i64 %C to i92
+; CHECK: ret i92 %D
+}
\ No newline at end of file