
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
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; RUN: opt < %s -passes=instcombine -S | FileCheck %s
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target datalayout = "e-m:e-i64:64-n8:16:32:64"
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; Although i1 is not in the datalayout, we should treat it
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; as a legal type because it is a fundamental type in IR.
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; This means we should shrink the phi (sink the zexts).
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define i64 @sink_i1_casts(i1 %cond1, i1 %cond2, i1 %cond) {
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; CHECK-LABEL: define i64 @sink_i1_casts(
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; CHECK-SAME: i1 [[COND1:%.*]], i1 [[COND2:%.*]], i1 [[COND:%.*]]) {
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; CHECK-NEXT: [[ENTRY:.*]]:
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; CHECK-NEXT: br i1 [[COND]], label %[[IF:.*]], label %[[END:.*]]
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; CHECK: [[IF]]:
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; CHECK-NEXT: br label %[[END]]
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; CHECK: [[END]]:
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; CHECK-NEXT: [[PHI_IN1:%.*]] = phi i1 [ [[COND1]], %[[ENTRY]] ], [ [[COND2]], %[[IF]] ]
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; CHECK-NEXT: [[PHI_IN:%.*]] = zext i1 [[PHI_IN1]] to i64
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; CHECK-NEXT: ret i64 [[PHI_IN]]
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;
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entry:
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%z1 = zext i1 %cond1 to i64
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br i1 %cond, label %if, label %end
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if:
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%z2 = zext i1 %cond2 to i64
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br label %end
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end:
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%phi = phi i64 [ %z1, %entry ], [ %z2, %if ]
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ret i64 %phi
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}
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