[CodeGenPrepare] Refine the cost model provided by the promotion helper.

- Use TargetLowering to check for the actual cost of each extension.
- Provide a factorized method to check for the cost of an extension:
  TargetLowering::isExtFree.
- Provide a virtual method TargetLowering::isExtFreeImpl for targets to be able
  to tune the cost of non-free extensions.

This refactoring offers a better granularity to model what really happens on
different targets.

No performance changes and very few code differences.

Part of <rdar://problem/19267165> 

llvm-svn: 231855

2 files changed, 32 insertions, 3 deletions

diff --git a/llvm/test/CodeGen/X86/codegen-prepare-addrmode-sext.ll b/llvm/test/CodeGen/X86/codegen-prepare-addrmode-sext.ll
index ac5cbb912aa..f00c40ba3a9 100644
--- a/llvm/test/CodeGen/X86/codegen-prepare-addrmode-sext.ll
+++ b/llvm/test/CodeGen/X86/codegen-prepare-addrmode-sext.ll
@@ -90,9 +90,7 @@ define i8 @oneArgPromotionZExt(i8 %arg1, i8* %base) {
 ; rolled back.
 ; Still, this test case exercises the desired code path.
 ; CHECK-LABEL: @oneArgPromotionCstZExt
-; CHECK: [[ZEXT:%[a-zA-Z_0-9-]+]] = zext i16 undef to i32
-; CHECK: [[SEXT:%[a-zA-Z_0-9-]+]] = sext i32 [[ZEXT]] to i64
-; CHECK: [[PROMOTED:%[a-zA-Z_0-9-]+]] = add nsw i64 [[SEXT]], 1
+; CHECK: [[PROMOTED:%[a-zA-Z_0-9-]+]] = add nsw i64 0, 1
 ; CHECK: getelementptr inbounds i8, i8* %base, i64 [[PROMOTED]]
 ; CHECK: ret
 define i8 @oneArgPromotionCstZExt(i8* %base) {
diff --git a/llvm/test/CodeGen/X86/codegen-prepare-extload.ll b/llvm/test/CodeGen/X86/codegen-prepare-extload.ll
index 6619ebec2f8..325b12e961e 100644
--- a/llvm/test/CodeGen/X86/codegen-prepare-extload.ll
+++ b/llvm/test/CodeGen/X86/codegen-prepare-extload.ll
@@ -361,3 +361,34 @@ entry:
   %conv3 = sext i16 %add to i32
   ret i32 %conv3
 }
+
+; Check that we see that one zext can be derived from the other for free.
+; OPTALL-LABEL: @promoteTwoArgZextWithSourceExtendedTwice
+; OPTALL: [[LD:%[a-zA-Z_0-9-]+]] = load i8, i8* %p
+
+; OPT-NEXT: [[ZEXT64:%[a-zA-Z_0-9-]+]] = zext i8 [[LD]] to i64
+; OPT-NEXT: [[ZEXT32:%[a-zA-Z_0-9-]+]] = zext i8 [[LD]] to i32
+; OPT-NEXT: [[RES32:%[a-zA-Z_0-9-]+]] = add nuw i32 [[ZEXT32]], %b
+; OPT-NEXT: [[RES64:%[a-zA-Z_0-9-]+]] = add nuw i64 [[ZEXT64]], 12
+; OPT-NEXT: store i32 [[RES32]], i32* %addr
+; OPT-NEXT: store i64 [[RES64]], i64* %q
+;
+; DISABLE-NEXT: [[ZEXT32:%[a-zA-Z_0-9-]+]] = zext i8 [[LD]] to i32
+; DISABLE-NEXT: [[RES32:%[a-zA-Z_0-9-]+]] = add nuw i32 [[ZEXT32]], %b
+; DISABLE-NEXT: [[RES2_32:%[a-zA-Z_0-9-]+]] = add nuw i32 [[ZEXT32]], 12
+; DISABLE-NEXT: store i32 [[RES32]], i32* %addr
+; DISABLE-NEXT: [[ZEXT64:%[a-zA-Z_0-9-]+]] = zext i32 [[RES2_32]] to i64
+; DISABLE-NEXT: store i64 [[ZEXT64]], i64* %q
+;
+; OPTALL-NEXT: ret void
+define void @promoteTwoArgZextWithSourceExtendedTwice(i8* %p, i64* %q, i32 %b, i32* %addr) {
+entry:
+  %t = load i8, i8* %p
+  %zextt = zext i8 %t to i32
+  %add = add nuw i32 %zextt, %b
+  %add2 = add nuw i32 %zextt, 12
+  store i32 %add, i32 *%addr
+  %s = zext i32 %add2 to i64
+  store i64 %s, i64* %q
+  ret void
+}