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Make skipping of vardecls more precise: it's ok to skip a decl if the entire

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compound stmt containing the decl is skipped.

llvm-svn: 126639
This commit is contained in:
Chris Lattner 2011-02-28 07:22:44 +00:00
parent 62208c395a
commit 35d3ac5e9e
2 changed files with 38 additions and 3 deletions
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21
clang/lib/CodeGen/CGStmt.cpp
View File

@ -887,9 +887,16 @@ static CSFC_Result CollectStatementsForCase(const Stmt *S,
// the skipped statements must be skippable) or we might already have it.
CompoundStmt::const_body_iterator I = CS->body_begin(), E = CS->body_end();
if (Case) {
// Keep track of whether we see a skipped declaration. The code could be
// using the declaration even if it is skipped, so we can't optimize out
// the decl if the kept statements might refer to it.
bool HadSkippedDecl = false;
// If we're looking for the case, just see if we can skip each of the
// substatements.
for (; Case && I != E; ++I) {
HadSkippedDecl |= isa<DeclStmt>(I);
switch (CollectStatementsForCase(*I, Case, FoundCase, ResultStmts)) {
case CSFC_Failure: return CSFC_Failure;
case CSFC_Success:
@ -898,6 +905,11 @@ static CSFC_Result CollectStatementsForCase(const Stmt *S,
// and also contains the break to exit the switch. In the later case,
// we just verify the rest of the statements are elidable.
if (FoundCase) {
// If we found the case and skipped declarations, we can't do the
// optimization.
if (HadSkippedDecl)
return CSFC_Failure;
for (++I; I != E; ++I)
if (CodeGenFunction::ContainsLabel(*I, true))
return CSFC_Failure;
@ -911,6 +923,11 @@ static CSFC_Result CollectStatementsForCase(const Stmt *S,
assert(FoundCase && "Didn't find case but returned fallthrough?");
// We recursively found Case, so we're not looking for it anymore.
Case = 0;
// If we found the case and skipped declarations, we can't do the
// optimization.
if (HadSkippedDecl)
return CSFC_Failure;
break;
}
}
@ -943,9 +960,7 @@ static CSFC_Result CollectStatementsForCase(const Stmt *S,
// for statement or increment etc. If we are skipping over this statement,
// just verify it doesn't have labels, which would make it invalid to elide.
if (Case) {
if (CodeGenFunction::ContainsLabel(S, true) ||
// Don't skip over DeclStmts, which can be used even if skipped over.
isa<DeclStmt>(S))
if (CodeGenFunction::ContainsLabel(S, true))
return CSFC_Failure;
return CSFC_Success;
}

20
clang/test/CodeGen/switch-dce.c
View File

@ -87,6 +87,7 @@ void test5() {
int x; // eliding var decl?
case 1:
x = 4;
i = x;
break;
}
}
@ -196,3 +197,22 @@ void test11() {
break;
}
}
// CHECK: @test12
// CHECK-NOT: switch
// CHECK: ret void
void test12() {
switch (1) {
case 2: {
int a; // Ok to skip this vardecl.
a = 42;
}
case 1:
break;
case 42: ;
int x; // eliding var decl?
x = 4;
break;
}
}