[llvm] [FastISel] Give PHI incoming materializations a debug location (PR #223677)

[via llvm-commits]

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+; RUN: llc -O0 %s -o - | FileCheck %s
+
+;; A loop header's PHI nodes are set up in the predecessor. When every incoming
+;; value is a constant, that code used to be left without a source location, so
+;; the loop's line got its first is_stmt entry inside the header. The header is
+;; also the target of the back edge, so a breakpoint on that line was hit once
+;; per iteration. This is the shape flang emits for a whole-array assignment,
+;;   integer :: arr(4)
+;;   arr = 11
+
+;; A loop the function falls into: everything from the first block label onwards
+;; belongs to it, so prologue_end has to be reached before one is seen.
+; CHECK-LABEL: fill_local_:
+; CHECK-NOT:   {{^\.LBB}}
+; CHECK:       .loc {{[0-9]+}} 3 3 prologue_end
+
+;; The same through a dummy argument, which reproduces once the loop has been
+;; rotated and the induction variable starts from a negative constant.
+; CHECK-LABEL: fill_arg_:
+; CHECK-NOT:   {{^\.LBB}}
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jeanPerier wrote:

Updated test does not rely on -NOT checks.

https://github.com/llvm/llvm-project/pull/223677