[InstCombine] do not shrink switch conditions to illegal types (PR29009)

This patch makes shrinking switch conditions less aggressive which was introduced by:
rL274233

Note that we have 2 new bugs to track potential follow-ups that might have solved PR29009
in different ways:
https://bugs.llvm.org/show_bug.cgi?id=39569
https://bugs.llvm.org/show_bug.cgi?id=39578

Patch by:
@dendibakh (Denis Bakhvalov)

Differential Revision: https://reviews.llvm.org/D54115

llvm-svn: 346315
This commit is contained in:
Sanjay Patel 2018-11-07 14:12:41 +00:00
parent 5e09c49499
commit 7552d0d2e6
2 changed files with 66 additions and 10 deletions

View File

@ -2510,9 +2510,11 @@ Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
unsigned NewWidth = Known.getBitWidth() - std::max(LeadingKnownZeros, LeadingKnownOnes);
// Shrink the condition operand if the new type is smaller than the old type.
// This may produce a non-standard type for the switch, but that's ok because
// the backend should extend back to a legal type for the target.
if (NewWidth > 0 && NewWidth < Known.getBitWidth()) {
// But do not shrink to a non-standard type, because backend can't generate
// good code for that yet.
// TODO: We can make it agressive again after fixing PR39569.
if (NewWidth > 0 && NewWidth < Known.getBitWidth() &&
shouldChangeType(Known.getBitWidth(), NewWidth)) {
IntegerType *Ty = IntegerType::get(SI.getContext(), NewWidth);
Builder.SetInsertPoint(&SI);
Value *NewCond = Builder.CreateTrunc(Cond, Ty, "trunc");

View File

@ -3,9 +3,6 @@
; RUN: opt < %s -instcombine -S -data-layout=n32 | FileCheck %s --check-prefix=ALL --check-prefix=CHECK32
; RUN: opt < %s -instcombine -S -data-layout=n32:64 | FileCheck %s --check-prefix=ALL --check-prefix=CHECK64
; In all cases, the data-layout is irrelevant. We should shrink as much as possible in InstCombine
; and allow the backend to expand as much as needed to ensure optimal codegen for any target.
define i32 @positive1(i64 %a) {
; ALL-LABEL: @positive1(
; ALL: switch i32
@ -102,13 +99,19 @@ return:
; Make sure to avoid assertion crashes and use the type before
; truncation to generate the sub constant expressions that leads
; to the recomputed condition.
; We allow to truncate from i64 to i59 if in 32-bit mode,
; because both are illegal.
define void @trunc64to59(i64 %a) {
; ALL-LABEL: @trunc64to59(
; ALL: switch i59
; ALL-NEXT: i59 0, label %sw.bb1
; ALL-NEXT: i59 18717182647723699, label %sw.bb2
; ALL-NEXT: ]
; ALL-CHECK32: switch i59
; ALL-CHECK32-NEXT: i59 0, label %sw.bb1
; ALL-CHECK32-NEXT: i59 18717182647723699, label %sw.bb2
; ALL-CHECK32-NEXT: ]
; ALL-CHECK64: switch i64
; ALL-CHECK64-NEXT: i64 0, label %sw.bb1
; ALL-CHECK64-NEXT: i64 18717182647723699, label %sw.bb2
; ALL-CHECK64-NEXT: ]
;
entry:
%tmp0 = and i64 %a, 15
@ -206,3 +209,54 @@ return: ; preds = %sw.epilog, %sw.bb2,
ret i32 %rval
}
; https://llvm.org/bugs/show_bug.cgi?id=29009
@a = global i32 0, align 4
@njob = global i32 0, align 4
declare i32 @goo()
; Make sure we do not shrink to illegal types (i3 in this case)
; if original type is legal (i32 in this case)
define void @PR29009() {
; ALL-LABEL: @PR29009(
; ALL: switch i32
; ALL-NEXT: i32 0, label
; ALL-NEXT: i32 3, label
; ALL-NEXT: ]
;
br label %1
; <label>:1: ; preds = %10, %0
%2 = load volatile i32, i32* @njob, align 4
%3 = icmp ne i32 %2, 0
br i1 %3, label %4, label %11
; <label>:4: ; preds = %1
%5 = call i32 @goo()
%6 = and i32 %5, 7
switch i32 %6, label %7 [
i32 0, label %8
i32 3, label %9
]
; <label>:7: ; preds = %4
store i32 6, i32* @a, align 4
br label %10
; <label>:8: ; preds = %4
store i32 1, i32* @a, align 4
br label %10
; <label>:9: ; preds = %4
store i32 2, i32* @a, align 4
br label %10
; <label>:10: ; preds = %13, %12, %11, %10, %9, %8, %7
br label %1
; <label>:11: ; preds = %1
ret void
}