[DAGCombine] fp_to_sint isSaturatingMinMax

Recommitting after fixing scalable vector crash.

Check for single smax pattern against zero when converting from a
small enough float.

Differential Revision: https://reviews.llvm.org/D142481

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Support/APFloat.cpp b/llvm/lib/Support/APFloat.cpp
index 9a8feba..e9998d7 100644
--- a/llvm/lib/Support/APFloat.cpp
+++ b/llvm/lib/Support/APFloat.cpp
@@ -251,6 +251,16 @@ namespace llvm {
   unsigned int APFloatBase::semanticsSizeInBits(const fltSemantics &semantics) {
     return semantics.sizeInBits;
   }
+  unsigned int APFloatBase::semanticsIntSizeInBits(const fltSemantics &semantics,
+                                                   bool isSigned) {
+    // The max FP value is pow(2, MaxExponent) * (1 + MaxFraction), so we need
+    // at least one more bit than the MaxExponent to hold the max FP value.
+    unsigned int MinBitWidth = semanticsMaxExponent(semantics) + 1;
+    // Extra sign bit needed.
+    if (isSigned)
+      ++MinBitWidth;
+    return MinBitWidth;
+  }
 
   unsigned APFloatBase::getSizeInBits(const fltSemantics &Sem) {
     return Sem.sizeInBits;