[PowerPC] Eliminate sign- and zero-extensions if already sign- or zero-extended

This patch enables redundant sign- and zero-extension elimination in PowerPC MI Peephole pass.
If the input value of a sign- or zero-extension is known to be already sign- or zero-extended, the operation is redundant and can be eliminated.
One common case is sign-extensions for a method parameter or for a method return value; they must be sign- or zero-extended as defined in PPC ELF ABI. 
For example of the following simple code, two extsw instructions are generated before the invocation of int_func and before the return. With this patch, both extsw are eliminated.

void int_func(int);
void ii_test(int a) {
    if (a & 1) return int_func(a);
}

Such redundant sign- or zero-extensions are quite common in many programs; e.g. I observed about 60,000 occurrences of the elimination while compiling the LLVM+CLANG.

Differential Revision: https://reviews.llvm.org/D31319

llvm-svn: 315888

1 files changed, 1 insertions, 3 deletions

diff --git a/llvm/test/CodeGen/PowerPC/expand-isel.ll b/llvm/test/CodeGen/PowerPC/expand-isel.ll
index 84d17baf13a..76479705f02 100644
--- a/llvm/test/CodeGen/PowerPC/expand-isel.ll
+++ b/llvm/test/CodeGen/PowerPC/expand-isel.ll
@@ -215,9 +215,7 @@ cleanup:
 ; CHECK-LABEL: @testComplexISEL
 ; CHECK-DAG: [[LI:r[0-9]+]], 1
 ; CHECK-DAG: cmplwi [[LD:r[0-9]+]], 0
-; CHECK: beq cr0, [[EQ:.LBB[0-9_]+]]
-; CHECK: blr
-; CHECK: [[EQ]]
+; CHECK: bnelr cr0
 ; CHECK: xor [[XOR:r[0-9]+]]
 ; CHECK: cntlzd [[CZ:r[0-9]+]], [[XOR]]
 ; CHECK: rldicl [[SH:r[0-9]+]], [[CZ]], 58, 63