50cac24877
Summary: Clang's "asm goto" feature didn't initially support outputs constraints. That was the same behavior as gcc's implementation. The decision by gcc not to support outputs was based on a restriction in their IR regarding terminators. LLVM doesn't restrict terminators from returning values (e.g. 'invoke'), so it made sense to support this feature. Output values are valid only on the 'fallthrough' path. If an output value's used on an indirect branch, then it's 'poisoned'. In theory, outputs *could* be valid on the 'indirect' paths, but it's very difficult to guarantee that the original semantics would be retained. E.g. because indirect labels could be used as data, we wouldn't be able to split critical edges in situations where two 'callbr' instructions have the same indirect label, because the indirect branch's destination would no longer be the same. Reviewers: jyknight, nickdesaulniers, hfinkel Reviewed By: jyknight, nickdesaulniers Subscribers: MaskRay, rsmith, hiraditya, llvm-commits, cfe-commits, craig.topper, rnk Tags: #clang, #llvm Differential Revision: https://reviews.llvm.org/D69876
106 lines
3.7 KiB
C
106 lines
3.7 KiB
C
// REQUIRES: x86-registered-target
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// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -O0 -emit-llvm %s -o - | FileCheck %s
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// RUN: %clang_cc1 -triple i386-pc-linux-gnu -O0 -emit-llvm %s -o - | FileCheck %s
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int test1(int cond) {
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// CHECK-LABEL: define i32 @test1(
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// CHECK: callbr void asm sideeffect
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// CHECK: to label %asm.fallthrough [label %label_true, label %loop]
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// CHECK-LABEL: asm.fallthrough:
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asm volatile goto("testl %0, %0; jne %l1;" :: "r"(cond)::label_true, loop);
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asm volatile goto("testl %0, %0; jne %l2;" :: "r"(cond)::label_true, loop);
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// CHECK: callbr void asm sideeffect
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// CHECK: to label %asm.fallthrough1 [label %label_true, label %loop]
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// CHECK-LABEL: asm.fallthrough1:
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return 0;
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loop:
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return 0;
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label_true:
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return 1;
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}
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int test2(int cond) {
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// CHECK-LABEL: define i32 @test2(
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// CHECK: callbr i32 asm sideeffect
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// CHECK: to label %asm.fallthrough [label %label_true, label %loop]
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// CHECK-LABEL: asm.fallthrough:
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asm volatile goto("testl %0, %0; jne %l2;" : "=r"(cond) : "r"(cond) :: label_true, loop);
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asm volatile goto("testl %0, %0; jne %l3;" : "=r"(cond) : "r"(cond) :: label_true, loop);
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// CHECK: callbr i32 asm sideeffect
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// CHECK: to label %asm.fallthrough1 [label %label_true, label %loop]
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// CHECK-LABEL: asm.fallthrough1:
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return 0;
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loop:
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return 0;
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label_true:
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return 1;
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}
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int test3(int out1, int out2) {
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// CHECK-LABEL: define i32 @test3(
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// CHECK: callbr { i32, i32 } asm sideeffect
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// CHECK: to label %asm.fallthrough [label %label_true, label %loop]
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// CHECK-LABEL: asm.fallthrough:
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asm volatile goto("testl %0, %0; jne %l3;" : "=r"(out1), "=r"(out2) : "r"(out1) :: label_true, loop);
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asm volatile goto("testl %0, %0; jne %l4;" : "=r"(out1), "=r"(out2) : "r"(out1) :: label_true, loop);
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// CHECK: callbr { i32, i32 } asm sideeffect
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// CHECK: to label %asm.fallthrough2 [label %label_true, label %loop]
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// CHECK-LABEL: asm.fallthrough2:
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return 0;
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loop:
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return 0;
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label_true:
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return 1;
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}
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int test4(int out1, int out2) {
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// CHECK-LABEL: define i32 @test4(
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// CHECK: callbr { i32, i32 } asm sideeffect "jne ${3:l}", "={si},={di},r,X,X,0,1
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// CHECK: to label %asm.fallthrough [label %label_true, label %loop]
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// CHECK-LABEL: asm.fallthrough:
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if (out1 < out2)
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asm volatile goto("jne %l3" : "+S"(out1), "+D"(out2) : "r"(out1) :: label_true, loop);
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else
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asm volatile goto("jne %l5" : "+S"(out1), "+D"(out2) : "r"(out1), "r"(out2) :: label_true, loop);
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// CHECK: callbr { i32, i32 } asm sideeffect "jne ${5:l}", "={si},={di},r,r,X,X,0,1
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// CHECK: to label %asm.fallthrough2 [label %label_true, label %loop]
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// CHECK-LABEL: asm.fallthrough2:
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return out1 + out2;
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loop:
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return -1;
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label_true:
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return -2;
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}
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int test5(int addr, int size, int limit) {
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// CHECK-LABEL: define i32 @test5(
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// CHECK: callbr i32 asm "add $1,$0 ; jc ${3:l} ; cmp $2,$0 ; ja ${3:l} ; ", "=r,imr,imr,X,0
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// CHECK: to label %asm.fallthrough [label %t_err]
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// CHECK-LABEL: asm.fallthrough:
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asm goto(
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"add %1,%0 ; "
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"jc %l[t_err] ; "
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"cmp %2,%0 ; "
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"ja %l[t_err] ; "
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: "+r" (addr)
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: "g" (size), "g" (limit)
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: : t_err);
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return 0;
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t_err:
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return 1;
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}
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int test6(int out1) {
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// CHECK-LABEL: define i32 @test6(
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// CHECK: callbr i32 asm sideeffect "testl $0, $0; testl $1, $1; jne ${2:l}", "={si},r,X,X,0,{{.*}} i8* blockaddress(@test6, %label_true), i8* blockaddress(@test6, %landing)
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// CHECK: to label %asm.fallthrough [label %label_true, label %landing]
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// CHECK-LABEL: asm.fallthrough:
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// CHECK-LABEL: landing:
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int out2 = 42;
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asm volatile goto("testl %0, %0; testl %1, %1; jne %l2" : "+S"(out2) : "r"(out1) :: label_true, landing);
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landing:
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return out1 + out2;
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label_true:
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return -2;
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}
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