mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2025-01-10 18:34:09 +00:00
5c98f14b78
This optimization tries to convert switch instructions that are used to select a value with only 2 unique cases + default block
to a select or a couple of selects (depending if the default block is reachable or not).
The typical case this optimization wants to be able to optimize is this one:
Example:
switch (a) {
case 10: %0 = icmp eq i32 %a, 10
return 10; %1 = select i1 %0, i32 10, i32 4
case 20: ----> %2 = icmp eq i32 %a, 20
return 2; %3 = select i1 %2, i32 2, i32 %1
default:
return 4;
}
It also sets the base for further optimizations that are planned and being reviewed.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219223 91177308-0d34-0410-b5e6-96231b3b80d8
73 lines
1.4 KiB
LLVM
73 lines
1.4 KiB
LLVM
; RUN: opt < %s -simplifycfg -S | FileCheck %s
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; int foo1_with_default(int a) {
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; switch(a) {
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; case 10:
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; return 10;
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; case 20:
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; return 2;
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; }
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; return 4;
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; }
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define i32 @foo1_with_default(i32 %a) {
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; CHECK-LABEL: @foo1_with_default
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; CHECK: %switch.selectcmp = icmp eq i32 %a, 20
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; CHECK-NEXT: %switch.select = select i1 %switch.selectcmp, i32 2, i32 4
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; CHECK-NEXT: %switch.selectcmp1 = icmp eq i32 %a, 10
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; CHECK-NEXT: %switch.select2 = select i1 %switch.selectcmp1, i32 10, i32 %switch.select
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entry:
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switch i32 %a, label %sw.epilog [
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i32 10, label %sw.bb
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i32 20, label %sw.bb1
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]
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sw.bb:
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br label %return
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sw.bb1:
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br label %return
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sw.epilog:
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br label %return
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return:
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%retval.0 = phi i32 [ 4, %sw.epilog ], [ 2, %sw.bb1 ], [ 10, %sw.bb ]
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ret i32 %retval.0
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}
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; int foo1_without_default(int a) {
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; switch(a) {
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; case 10:
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; return 10;
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; case 20:
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; return 2;
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; }
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; __builtin_unreachable();
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; }
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define i32 @foo1_without_default(i32 %a) {
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; CHECK-LABEL: @foo1_without_default
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; CHECK: %switch.selectcmp = icmp eq i32 %a, 10
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; CHECK-NEXT: %switch.select = select i1 %switch.selectcmp, i32 10, i32 2
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; CHECK-NOT: %switch.selectcmp1
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entry:
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switch i32 %a, label %sw.epilog [
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i32 10, label %sw.bb
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i32 20, label %sw.bb1
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]
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sw.bb:
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br label %return
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sw.bb1:
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br label %return
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sw.epilog:
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unreachable
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return:
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%retval.0 = phi i32 [ 2, %sw.bb1 ], [ 10, %sw.bb ]
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ret i32 %retval.0
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}
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