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Fix a bad overflow check pointed out by Ben.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185226 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen
2013-06-28 21:51:18 +00:00
parent 9e638df937
commit 5d3257e37c
2 changed files with 7 additions and 4 deletions
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6
lib/Support/BlockFrequency.cpp
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@ -47,9 +47,7 @@ static uint64_t div96bit(uint64_t W[2], uint32_t D) {
uint64_t x = W[1]; uint64_t x = W[1];
unsigned i; unsigned i;
// This is really a 64-bit division. assert(x != 0 && "This is really a 64-bit division");
if (!x)
return y / D;
// This long division algorithm automatically saturates on overflow. // This long division algorithm automatically saturates on overflow.
for (i = 0; i < 64 && x; ++i) { for (i = 0; i < 64 && x; ++i) {
@ -75,7 +73,7 @@ void BlockFrequency::scale(uint32_t N, uint32_t D) {
uint64_t MulRes = (MulHi << 32) + MulLo; uint64_t MulRes = (MulHi << 32) + MulLo;
// If the product fits in 64 bits, just use built-in division. // If the product fits in 64 bits, just use built-in division.
if (MulHi <= UINT32_MAX && MulRes <= MulLo) { if (MulHi <= UINT32_MAX && MulRes >= MulLo) {
Frequency = MulRes / D; Frequency = MulRes / D;
return; return;
} }

5
unittests/Support/BlockFrequencyTest.cpp
View File

@ -68,6 +68,11 @@ TEST(BlockFrequencyTest, Saturate) {
Freq = 0x1000000000000000ULL; Freq = 0x1000000000000000ULL;
Freq /= BranchProbability(10000, 160000); Freq /= BranchProbability(10000, 160000);
EXPECT_EQ(Freq.getFrequency(), UINT64_MAX); EXPECT_EQ(Freq.getFrequency(), UINT64_MAX);
// Try to cheat the multiplication overflow check.
Freq = 0x00000001f0000001ull;
Freq /= BranchProbability(1000, 0xf000000f);
EXPECT_EQ(33506781356485509ULL, Freq.getFrequency());
} }
TEST(BlockFrequencyTest, ProbabilityCompare) { TEST(BlockFrequencyTest, ProbabilityCompare) {