Fix Phi elimination pass sometimes leaving broken insts in release builds (#7499)

* Make phi elimination pass modify branches in-place

* Add test and fix formatting

* Avoid double removal of param insts

2 files changed, 31 insertions, 0 deletions

diff --git a/tests/bugs/gh-7499.slang b/tests/bugs/gh-7499.slang
new file mode 100644
index 000000000..ea5432758
--- /dev/null
+++ b/tests/bugs/gh-7499.slang
@@ -0,0 +1,26 @@
+//TEST:EXECUTABLE:
+[mutating]
+public void f(Ptr<int> arr, inout int size)
+{
+    for (int i = 0; i < 1; ++i)
+        arr[i] = 0;
+
+    int end = 0;
+    if (end >= size)
+        end = size;
+
+    for (int i = 0; i < 1; ++i)
+        arr[i] = 0;
+
+    size -= end;
+}
+
+export __extern_cpp int main()
+{
+    // Success is not crashing the compiler.
+    int size = 0;
+    int arr = 0;
+    f(&arr, size);
+
+    return 0;
+}
diff --git a/tests/bugs/gh-7499.slang.expected b/tests/bugs/gh-7499.slang.expected
new file mode 100644
index 000000000..4c32e2510
--- /dev/null
+++ b/tests/bugs/gh-7499.slang.expected
@@ -0,0 +1,5 @@
+result code = 0
+standard error = {
+}
+standard output = {
+}