Benjamin Kramer fded9fa4a4 [RemoveDuplicatePHINodes] Start over after removing a PHI. ... This makes RemoveDuplicatePHINodes more effective and fixes an assertion failure. Triggering the assertions requires a DenseSet reallocation so this change only contains a constructive test. I'll explain the issue with a small example. In the following function there's a duplicate PHI, %4 and %5 are identical. When this is found the DenseSet in RemoveDuplicatePHINodes contains %2, %3 and %4. define void @F() { br label %1 ; <label>:1 ; preds = %1, %0 %2 = phi i32 [ 42, %0 ], [ %4, %1 ] %3 = phi i32 [ 42, %0 ], [ %5, %1 ] %4 = phi i32 [ 42, %0 ], [ 23, %1 ] %5 = phi i32 [ 42, %0 ], [ 23, %1 ] br label %1 } after RemoveDuplicatePHINodes runs the function looks like this. %3 has changed and is now identical to %2, but RemoveDuplicatePHINodes never saw this. define void @F() { br label %1 ; <label>:1 ; preds = %1, %0 %2 = phi i32 [ 42, %0 ], [ %4, %1 ] %3 = phi i32 [ 42, %0 ], [ %4, %1 ] %4 = phi i32 [ 42, %0 ], [ 23, %1 ] br label %1 } If the DenseSet does a reallocation now it will reinsert all keys and stumble over %3 now having a different hash value than it had when inserted into the map for the first time. This change clears the set whenever a PHI is deleted and starts the progress from the beginning, allowing %3 to be deleted and avoiding inconsistent DenseSet state. This potentially has a negative performance impact because it rescans all PHIs, but I don't think that this ever makes a difference in practice. llvm-svn: 246694		2015-09-02 19:52:23 +00:00
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IPO
Utils	[RemoveDuplicatePHINodes] Start over after removing a PHI.	2015-09-02 19:52:23 +00:00
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