380fa875ab
This patch replaces all dominated uses of condition with true/false to
improve context-sensitive optimizations. It eliminates a bunch of
branches in llvm-opt-benchmark.
As a side effect, it may introduce new phi nodes in some corner cases.
See the following case:
```
define i1 @test(i1 %cmp, i1 %cond) {
entry:
br i1 %cond, label %bb1, label %bb2
bb1:
br i1 %cmp, label %if.then, label %if.else
if.then:
br %bb2
if.else:
br %bb2
bb2:
%res = phi i1 [%cmp, %entry], [%cmp, %if.then], [%cmp, %if.else]
ret i1 %res
}
```
It will be simplified into:
```
define i1 @test(i1 %cmp, i1 %cond) {
entry:
br i1 %cond, label %bb1, label %bb2
bb1:
br i1 %cmp, label %if.then, label %if.else
if.then:
br %bb2
if.else:
br %bb2
bb2:
%res = phi i1 [%cmp, %entry], [true, %if.then], [false, %if.else]
ret i1 %res
}
```
I am planning to fix this in late pipeline/CGP since this problem exists
before the patch.
35 lines
1.1 KiB
LLVM
35 lines
1.1 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
|
|
; RUN: opt < %s -passes=instcombine -S | FileCheck %s
|
|
|
|
target datalayout = "e-m:e-i64:64-n8:16:32:64"
|
|
|
|
; Although i1 is not in the datalayout, we should treat it
|
|
; as a legal type because it is a fundamental type in IR.
|
|
; This means we should shrink the phi (sink the zexts).
|
|
|
|
define i64 @sink_i1_casts(i1 %cond1, i1 %cond2, i1 %cond) {
|
|
; CHECK-LABEL: define i64 @sink_i1_casts(
|
|
; CHECK-SAME: i1 [[COND1:%.*]], i1 [[COND2:%.*]], i1 [[COND:%.*]]) {
|
|
; CHECK-NEXT: [[ENTRY:.*]]:
|
|
; CHECK-NEXT: br i1 [[COND]], label %[[IF:.*]], label %[[END:.*]]
|
|
; CHECK: [[IF]]:
|
|
; CHECK-NEXT: br label %[[END]]
|
|
; CHECK: [[END]]:
|
|
; CHECK-NEXT: [[PHI_IN1:%.*]] = phi i1 [ [[COND1]], %[[ENTRY]] ], [ [[COND2]], %[[IF]] ]
|
|
; CHECK-NEXT: [[PHI_IN:%.*]] = zext i1 [[PHI_IN1]] to i64
|
|
; CHECK-NEXT: ret i64 [[PHI_IN]]
|
|
;
|
|
entry:
|
|
%z1 = zext i1 %cond1 to i64
|
|
br i1 %cond, label %if, label %end
|
|
|
|
if:
|
|
%z2 = zext i1 %cond2 to i64
|
|
br label %end
|
|
|
|
end:
|
|
%phi = phi i64 [ %z1, %entry ], [ %z2, %if ]
|
|
ret i64 %phi
|
|
}
|
|
|