slow validate failure: IntegerToFloat different result optllvm

Reproduce with

hadrian/build test --freeze1  --docs=none --flavour=slow-validate --test-speed=slow --only="IntegerToFloat"

+++ "/run/user/1000/ghctest-derda1up/test   spaces/testsuite/tests/numeric/should_run/IntegerToFloat.run/IntegerToFloat.run.stdout.normalised"	2022-08-05 18:05:17.563600812 +0100
@@ -17,7 +17,7 @@
 0x1p36
 0x1.fffffcp59
 0x1p60
-0x1.fffffep59
+0x1p60
 0x1p60
 0x1.fffffcp63
 0x1p64
*** unexpected failure for IntegerToFloat(optllvm)

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