[PATCH] Fix PR88792

[Richard Biener]

The following avoids a value-number as leader during PRE PHI translation
since that exposes us to bogus flow-sensitive info.

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

Richard.

>From d4849ecb2e82e49df4490d92f33c24a851f6e195 Mon Sep 17 00:00:00 2001
From: Richard Guenther <rguenther@suse.de>
Date: Thu, 10 Jan 2019 13:34:01 +0100
Subject: [PATCH] fix-pr88792

2019-01-10  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/88792
	* tree-ssa-pre.c (get_representative_for): Do not return a
	value-number here.

	* gcc.dg/torture/pr88792.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/torture/pr88792.c b/gcc/testsuite/gcc.dg/torture/pr88792.c
new file mode 100644
index 00000000000..e7f8fc0a624
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr88792.c
@@ -0,0 +1,32 @@
+/* { dg-do run } */
+
+int one = 1;
+
+char
+__attribute__((noipa))
+foo(char v)
+{
+  int modec;
+
+  if (one)
+    {
+      modec = ((v < 'A' || v > 'Z') ? v : v + ('a' - 'A'));
+      if (modec != 't' && modec != 'c' && modec != 'g')
+	modec = 0;
+    }
+  else
+    modec = 'g';
+
+  return modec;
+}
+
+int main(int argc, char **argv)
+{
+  char c = 't';
+  int r = foo (c);
+
+  if (r != c)
+    __builtin_abort ();
+
+  return 0;
+}
diff --git a/gcc/tree-ssa-pre.c b/gcc/tree-ssa-pre.c
index a37eff6c7e3..3f38371cb21 100644
--- a/gcc/tree-ssa-pre.c
+++ b/gcc/tree-ssa-pre.c
@@ -1262,7 +1262,7 @@ get_representative_for (const pre_expr e, basic_block b = NULL)
   switch (e->kind)
     {
     case NAME:
-      return VN_INFO (PRE_EXPR_NAME (e))->valnum;
+      return PRE_EXPR_NAME (e);
     case CONSTANT:
       return PRE_EXPR_CONSTANT (e);
     case NARY: