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Hi, The problem here is that forward prop can cause an aliasing problem that did not exist in the original source. So currently we transform *(*int)&a->float_field into VIEW_CONVERT_EXPR<int>(a->float_field). This causes an aliasing issue if the aliasing sets of int and float don't overlap. So we want to disable this transformation if the inner most reference is an INDIRECT_REF and the aliasing sets don't match or the aliasing set for the access of the INDIRECT_REF will be 0. Just disabling it for all INDIRECT_REFs will disabling some optimizations when the aliasing sets are the same and the VIEW_CONVERT_EXPR could be changed into a NOP_EXPR (think unsigned int and signed int, I added a testcase for that). OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions. Thanks, Andrew Pinski * tree-ssa-forwprop.c (forward_propagate_addr_expr_1): Disable the VCE conversion if the base address is an indirect reference and the aliasing sets could cause issues. * gcc.dg/tree-ssa/struct-aliasing-1.c: New test. * gcc.dg/tree-ssa/struct-aliasing-2.c: New test. * gcc.c-torture/execute/struct-aliasing-1.c: New test.
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