[InstCombine] Add tests for indirect mul by power of 2; NFC

[nikic]

llvm/test/Transforms/InstCombine/mul-pow2.ll

64

Missing a commuted test -- everything here gets canonicalized to mul s, x.

Also missing a multi-use test. This is going to fail (as in, perform an unprofitable transform) due to open FIXMEs in takeLog2(), but we should at least highlight that the problem exists.

[goldstein.w.n]

Put tests in canonical commuted form. Add multiuse tests

[goldstein.w.n]

Add flag propegation test

[nikic]

LGTM

[goldstein.w.n]

Rebase

llvm/test/Transforms/InstCombine/mul-pow2.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=instcombine -S < %s | FileCheck %s
+declare void @use_i8(i8)
+define i8 @mul_selectp2_x(i8 %x, i1 %c) {
+; CHECK-LABEL: @mul_selectp2_x(
+; CHECK-NEXT:    [[S:%.*]] = select i1 [[C:%.*]], i8 2, i8 4
+; CHECK-NEXT:    [[R:%.*]] = mul i8 [[S]], [[X:%.*]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %s = select i1 %c, i8 2, i8 4
+  %r = mul i8 %s, %x
+  ret i8 %r
+}
+
+define i8 @mul_selectp2_x_multiuse_fixme(i8 %x, i1 %c) {
+; CHECK-LABEL: @mul_selectp2_x_multiuse_fixme(
+; CHECK-NEXT:    [[S:%.*]] = select i1 [[C:%.*]], i8 2, i8 4
+; CHECK-NEXT:    [[R:%.*]] = mul i8 [[S]], [[X:%.*]]
+; CHECK-NEXT:    call void @use_i8(i8 [[S]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %s = select i1 %c, i8 2, i8 4
+  %r = mul i8 %s, %x
+  call void @use_i8(i8 %s)
+  ret i8 %r
+}
+
+define i8 @mul_selectp2_x_non_const(i8 %x, i1 %c, i8 %yy) {
+; CHECK-LABEL: @mul_selectp2_x_non_const(
+; CHECK-NEXT:    [[Y:%.*]] = shl nuw i8 1, [[YY:%.*]]
+; CHECK-NEXT:    [[S:%.*]] = select i1 [[C:%.*]], i8 2, i8 [[Y]]
+; CHECK-NEXT:    [[R:%.*]] = mul i8 [[S]], [[X:%.*]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %y = shl i8 1, %yy
+  %s = select i1 %c, i8 2, i8 %y
+  %r = mul i8 %s, %x
+  ret i8 %r
+}
+
+define i8 @mul_selectp2_x_non_const_multiuse(i8 %x, i1 %c, i8 %yy) {
+; CHECK-LABEL: @mul_selectp2_x_non_const_multiuse(
+; CHECK-NEXT:    [[Y:%.*]] = shl nuw i8 1, [[YY:%.*]]
+; CHECK-NEXT:    [[S:%.*]] = select i1 [[C:%.*]], i8 2, i8 [[Y]]
+; CHECK-NEXT:    [[R:%.*]] = mul i8 [[S]], [[X:%.*]]
+; CHECK-NEXT:    call void @use_i8(i8 [[Y]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %y = shl i8 1, %yy
+  %s = select i1 %c, i8 2, i8 %y
+  %r = mul i8 %s, %x
+  call void @use_i8(i8 %y)
+  ret i8 %r
+}
+
+define i8 @mul_x_selectp2(i8 %xx, i1 %c) {
+; CHECK-LABEL: @mul_x_selectp2(
+; CHECK-NEXT:    [[X:%.*]] = mul i8 [[XX:%.*]], [[XX]]
+; CHECK-NEXT:    [[S:%.*]] = select i1 [[C:%.*]], i8 8, i8 1
+; CHECK-NEXT:    [[R:%.*]] = mul i8 [[X]], [[S]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %x = mul i8 %xx, %xx
+  %s = select i1 %c, i8 8, i8 1
+  %r = mul i8 %x, %s
+  ret i8 %r
+}
+
+define i8 @mul_select_nonp2_x_fail(i8 %x, i1 %c) {
+; CHECK-LABEL: @mul_select_nonp2_x_fail(
+; CHECK-NEXT:    [[S:%.*]] = select i1 [[C:%.*]], i8 2, i8 5
+; CHECK-NEXT:    [[R:%.*]] = mul i8 [[S]], [[X:%.*]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %s = select i1 %c, i8 2, i8 5
+  %r = mul i8 %s, %x
+  ret i8 %r
+}
+
+define <2 x i8> @mul_x_selectp2_vec(<2 x i8> %xx, i1 %c) {
+; CHECK-LABEL: @mul_x_selectp2_vec(
+; CHECK-NEXT:    [[X:%.*]] = mul <2 x i8> [[XX:%.*]], [[XX]]
+; CHECK-NEXT:    [[S:%.*]] = select i1 [[C:%.*]], <2 x i8> <i8 8, i8 16>, <2 x i8> <i8 4, i8 1>
+; CHECK-NEXT:    [[R:%.*]] = mul <2 x i8> [[X]], [[S]]
+; CHECK-NEXT:    ret <2 x i8> [[R]]
+;
+  %x = mul <2 x i8> %xx, %xx
+  %s = select i1 %c, <2 x i8> <i8 8, i8 16>, <2 x i8> <i8 4, i8 1>
+  %r = mul <2 x i8> %x, %s
+  ret <2 x i8> %r
+}