[llvm-commits] [PATCH] InstCombine: remove malloc+free if malloc's only uses are comparisons to null

[Chris Lattner]

On May 20, 2010, at 9:04 PM, Matti Niemenmaa wrote:

> 
> Good catch, that's possible. It depends on how exactly Value::use_iterator works, which I don't know in enough detail. I did, however, find some code in Transforms/Scalar/SCCP.cpp which does an early increment to avoid such issues, so there probably is such a danger here.
> 
> Attached an amended patch with the cleanups and incrementing UI before the erases instead of after.

A couple more requests :)

+++ test/Transforms/InstCombine/malloc-free-delete2.ll	(revision 0)
@@ -0,0 +1,11 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+define i1 @foo() {
+; CHECK: @foo
+; CHECK-NEXT: ret i1 false
+  %m = call i8* @malloc(i64 1)
+  %z = icmp eq i8* %m, null
+  call void @free(i8* %m)
+  ret i1 %z
+}
+declare i8* @malloc(i64)
+declare void @free(i8*)

Please merge this into test/Transforms/InstCombine/malloc-free-delete.ll since it already uses filecheck, thanks!

+    if (const ICmpInst *ICI = dyn_cast<ICmpInst>(*UI)) {
+      ICmpInst::Predicate Pred = ICI->getPredicate();
+      if (Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE &&

Please use ICI->isEquality()

+          (isa<ConstantPointerNull>(ICI->getOperand(0)) ||
+           isa<ConstantPointerNull>(ICI->getOperand(1))))

comparisons against null will put the null on the RHS of the compare, just check operand #1.

If you feel like it, you could also generalize this to handle calloc/valloc as well.

Thanks for working on this!

-Chris